Magneto-resistance effect element magneto-resistance effect memory cell, MRAM, and method for performing information write to or read from the magneto-resistance effect memory cell

ABSTRACT

A magneto-resistive effect element includes a first ferromagnetic film; a second ferromagnetic film; and a first nonmagnetic film interposed between the first ferromagnetic film and the second ferromagnetic film. The first ferromagnetic film has a magnetization more easily rotatable than a magnetization of the second ferromagnetic film by an external magnetic field. The first ferromagnetic film has an effective magnetic thickness of about 2 nm or less.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention:

[0002] The present invention relates to a microscopic magneto-resistiveeffect element and a microscopic magneto-resistive effect memory cell,an MRAM including a plurality of such magneto-resistive effect elementsor a plurality of magneto-resistive effect memory cells integrated at ahigh density, and a method for performing information write or read toor from the microscopic magneto-resistive effect memory cell.

[0003] 2. Description of the Related Art:

[0004] A magnetic random access memory (MRAM) using a magneto-resistive(MR) film was proposed by L. J. Schwee, Proc. INTERMAG Conf. IEEE Trans.on Magn. Kyoto (1972) pp. 405. Various types of MRAMs including wordlines as current lines for generating a magnetic field and sense linesusing MR films for reading data have been studied. One of such studiesis described in A. V. Pohm et al., IEEE Trans. on Magn. 28 (1992) pp.2356. Such memory devices generally use an NiFe film or the likeexhibiting an anisotropic MR effect (AMR) having an MR change ratio ofabout 2%, and thus the level of an output signal needs to be improved.

[0005] M. N. Baibich et al., Phys. Rev. Lett. 61 (1988) pp. 2472describes that an artificial lattice film formed of magnetic filmsexchange-coupled through a nonmagnetic film to each other shows a giantMR effect (GMR). K. T. M. Ranmuthu et al., IEEE Trans. on Magn. 29(1993) pp. 2593 proposes an MRAM using a GMR film formed of magneticfilms antiferromagnetically exchanged-coupled to each other. The GMRfilm exhibits a relatively large MR change ratio, but disadvantageouslyrequires a larger magnetic field to be applied and thus requires alarger current for writing and reading information than an AMR film.

[0006] One exemplary type of non-coupling GMR film is a spin valve film.B. Dieny et al., J. Magn. Magn. Mater. 93 (1991) pp. 101 describes aspin valve film using an antiferromagnetic film. H. Sakakima et al.,Jpn. J. Appl. Phys. 33 (1994) pp. L1668 describes a spin valve filmusing a semi-hard magnetic film. These spin valve films require amagnetic field as small as that required by the AMR films and stillexhibit a larger MR change ratio than the AMR films. Y. Irie et al.,Jpn. J. Appl. Phys. 34 (1995) pp. L415 describes an MRAM, formed of aspin valve film using an antiferromagnetic film or a hard magnetic film,which performs a non-destructive read out (NDRO).

[0007] The nonmagnetic film used for the above-described GMR films is aconductive film formed of Cu or the like. Tunneling GMR films (TMR)using Al₂O₃, MgO or the like as the nonmagnetic film have actively beenstudied, and MRAMs using the TMR film have been proposed.

[0008] It is known that the MR effect provided when a current flowsperpendicular to the surface of a GMR film (CPPMR) is larger than the MReffect provided when a current flows parallel to the surface of the GMRfilm (CIPMR). A TMR film, which has a relatively high impedance, isexpected to provide a sufficiently large output.

[0009] However, reduction in the size of an MRAM generates the followingproblems. A magnetic film usually has a thickness of about 1 nm to about10 nm. In an MRAM having a width of on the order of submicrometers, thestrength of an anti-magnetic field component is not negligible, and thusa relatively large magnetic field is required to magnetize the magneticfilm. A relatively large magnetic coercive force is also required tomaintain the magnetized state of the magnetic film. Thus, it isdifficult to invert the magnetization by a magnetic field which isgenerated by a current flowing in word lines.

SUMMARY OF THE INVENTION

[0010] According to one aspect of the invention, a magneto-resistiveeffect element includes a first ferromagnetic film; a secondferromagnetic film: and a first nonmagnetic film interposed between thefirst ferromagnetic film and the second ferromagnetic film. The firstferromagnetic film has a magnetization more easily rotatable than amagnetization of the second ferromagnetic film by an external magneticfield. The first ferromagnetic film has an effective magnetic thicknessof about 2 nm or less.

[0011] In one embodiment of the invention, at least one of the firstferromagnetic film and the second ferromagnetic film has a magnetizationdirection in a planar direction thereof.

[0012] In one embodiment of the invention, the second ferromagnetic filmis formed of XMnSb, where X is at least one element selected from thegroup consisting of Ni, Pt, Pd and Cu.

[0013] In one embodiment of the invention, the first ferromagnetic filmincludes an amorphous magnetic film, and a third ferromagnetic film incontact with the first nonmagnetic film and interposed between theamorphous magnetic film and the first nonmagnetic film.

[0014] In one embodiment of the invention, the third ferromagnetic filmhas a thickness of about 0.2 nm or more and about 2 nm or less.

[0015] In one embodiment of the invention, the third ferromagnetic filmhas a thickness of about 0.8 nm or more and about 1.2 nm or less.

[0016] In one embodiment of the invention, the amorphous magnetic filmincludes at least one selected from the group consisting of CoFeB andCoMnB.

[0017] In one embodiment of the invention, the first ferromagnetic filmincludes a second nonmagnetic film, a fourth ferromagnetic film, and afifth ferromagnetic film. The fourth ferromagnetic film and the fifthferromagnetic film are antiferromagnetically exchange-coupled with eachother through the second nonmagnetic film.

[0018] In one embodiment of the invention, the fourth ferromagnetic filmand the fifth ferromagnetic film have different strengths of saturatedmagnetization from each other.

[0019] In one embodiment of the invention, the fourth ferromagnetic filmand the fifth ferromagnetic film have different thicknesses from eachother.

[0020] In one embodiment of the invention, the fourth ferromagnetic filmand the fifth ferromagnetic film have a thickness difference of about 2nm or less.

[0021] In one embodiment of the invention, the second nonmagnetic filmis formed of Ru.

[0022] In one embodiment of the invention, the second nonmagnetic filmis formed of one of Rh, Ir and Re.

[0023] In one embodiment of the invention, the second nonmagnetic filmhas a thickness of about 0.6 nm or more and about 0.8 nm or less.

[0024] In one embodiment of the invention, at least one of the fourthferromagnetic film and the fifth ferromagnetic film contains at leastone element selected from the group consisting of Ni, Co and Fe as amain component.

[0025] In one embodiment of the invention, the fourth ferromagnetic filmand the fifth ferromagnetic film are magnetization-rotated while beingkept anti-parallel to each other.

[0026] In one embodiment of the invention, the second ferromagnetic filmincludes a third nonmagnetic film, a sixth ferromagnetic film, and aseventh ferromagnetic film. The sixth ferromagnetic film and the seventhferromagnetic film are antiferromagnetically exchange-coupled with eachother through the third nonmagnetic film.

[0027] In one embodiment of the invention, the third nonmagnetic film isformed of Ru.

[0028] In one embodiment of the invention, the third nonmagnetic film isformed of one of Rh, Ir and Re.

[0029] In one embodiment of the invention, the third nonmagnetic filmhas a thickness of about 0.6 nm or more and about 0.8 nm or less.

[0030] In one embodiment of the invention, at least one of the sixthferromagnetic film and the seventh ferromagnetic film contains at leastone element selected from the group consisting of Ni, Co and Fe as amain component.

[0031] In one embodiment of the invention, the first nonmagnetic film isan insulating film.

[0032] In one embodiment of the invention, the insulating film containsat least one selected from the group consisting of Al₂O₃, MgO, a carbideand a nitride.

[0033] According to another aspect of the invention, a magneto-resistiveeffect memory cell includes a first ferromagnetic film; a secondferromagnetic film; a first nonmagnetic film interposed between thefirst ferromagnetic film and the second ferromagnetic film; and at leastone conductive film for causing a magnetization rotation of at least thefirst ferromagnetic film. The first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field. The firstferromagnetic film has an effective magnetic thickness of about 2 nm orless.

[0034] In one embodiment of the invention, at least one of the firstferromagnetic film and the second ferromagnetic film has a magnetizationdirection in a planar direction thereof.

[0035] In one embodiment of the invention, the second ferromagnetic filmis formed of XMnSb, where X is at least one element selected from thegroup consisting of Ni, Pt, Pd and Cu.

[0036] In one embodiment of the invention, the first ferromagnetic filmincludes an amorphous magnetic film, and a third ferromagnetic film incontact with the first nonmagnetic film and interposed between theamorphous magnetic film and the first nonmagnetic film.

[0037] In one embodiment of the invent ion, the third ferromagnetic filmhas a thickness of about 0.2 nm or more and about 2 nm or less.

[0038] In one embodiment of the invention, the third ferromagnetic filmhas a thickness of about 0.8 nm or more and about 1.2 nm or less.

[0039] In one embodiment of the invention, the amorphous magnetic filmincludes at least one selected from the group consisting of CoFeB andCoMnB.

[0040] In one embodiment of the invention, the first ferromagnetic filmincludes a second nonmagnetic film, a fourth ferromagnetic film, and afifth ferromagnetic film. The fourth ferromagnetic film and the fifthferromagnetic film are antiferromagnetically exchange-coupled with eachother through the second nonmagnetic film.

[0041] In one embodiment of the invention, the fourth ferromagnetic filmand the fifth ferromagnetic film have different strengths of saturatedmagnetization from each other.

[0042] In one embodiment of the invention, the fourth ferromagnetic filmand the fifth ferromagnetic film have different thicknesses from eachother.

[0043] In one embodiment of the invention, the fourth ferromagnetic filmand the fifth ferromagnetic film have a thickness difference of about 2nm or less.

[0044] In one embodiment of the invention, the second nonmagnetic filmis formed of Ru.

[0045] In one embodiment of the invention, the second nonmagnetic filmis formed of one of Rh, Ir and Re.

[0046] In one embodiment of the invention, the second nonmagnetic filmhas a thickness of about 0.6 nm or more and about 0.8 nm or less.

[0047] In one embodiment of the invention, at least one of the fourthferromagnetic film and the fifth ferromagnetic film contains at leastone element selected from the group consisting of Ni, Co and Fe as amain component.

[0048] In one embodiment of the invention, the fourth ferromagnetic filmand the fifth ferromagnetic film are magnetization-rotated while beingkept anti-parallel to each other.

[0049] In one embodiment of the invention, the second ferromagnetic filmincludes a third nonmagnetic film, a sixth ferromagnetic film, and aseventh ferromagnetic film. The sixth ferromagnetic film and the seventhferromagnetic film are antiferromagnetically exchange-coupled with eachother through the third nonmagnetic film.

[0050] In one embodiment of the invention, the third nonmagnetic film isformed of Ru.

[0051] In one embodiment of the invention, the third nonmagnetic film isformed of one of Rh, Ir and Re.

[0052] In one embodiment of the invention, the third nonmagnetic filmhas a thickness of about 0.6 nm or more and about 0.8 nm or less.

[0053] In one embodiment of the invention, at least one of the sixthferromagnetic film and the seventh ferromagnetic film contains at leastone element selected from the group consisting of Ni, Co and Fe as amain component.

[0054] In one embodiment of the invention, the first nonmagnetic film isan insulating film.

[0055] In one embodiment of the invention, the insulating film containsat least one selected from the group consisting of Al₂O₃, MgO, a carbideand a nitride.

[0056] In one embodiment of the invention, at least two layer structuresare provided, each layer structure including the first ferromagneticfilm, the second ferromagnetic film, and the first nonmagnetic filminterposed between the first ferromagnetic film and the secondferromagnetic film. The at least two layer structures are stacked withat least one fourth nonmagnetic film interposed therebetween.

[0057] In one embodiment of the invention, the second ferromagneticfilms of the at least two layer structures have different magneticcoercive forces from each other.

[0058] According to still another aspect of the invention, an MRAMincludes a plurality of the above-described magneto-resistive effectmemory cells. The plurality of conductive films are arranged in at leastone prescribed direction.

[0059] According to still another aspect of the invention, amagneto-resistive effect element includes a first ferromagnetic film; asecond ferromagnetic film; and a nonmagnetic film interposed between thefirst ferromagnetic film and the second ferromagnetic film. The firstferromagnetic film has a magnetization more easily rotatable than amagnetization of the second ferromagnetic film by an external magneticfield. The first ferromagnetic film includes an amorphous magnetic film,and a third ferromagnetic film in contact with the nonmagnetic film andinterposed between the amorphous magnetic film and the nonmagnetic film.

[0060] In one embodiment of the invention, at least one of the firstferromagnetic film and the second ferromagnetic film has a magnetizationdirection in a planar direction thereof.

[0061] In one embodiment of the invention, the nonmagnetic film is aninsulating film.

[0062] According to still another aspect of the invention, amagneto-resistive effect element includes a first ferromagnetic film; asecond ferromagnetic film; and a first nonmagnetic film interposedbetween the first ferromagnetic film and the second ferromagnetic film.The first ferromagnetic film has a magnetization more easily rotatablethan a magnetization of the second ferromagnetic film by an externalmagnetic field. The first ferromagnetic film includes a secondnonmagnetic film, a third ferromagnetic film, and a fourth ferromagneticfilm. The third ferromagnetic film and the fourth ferromagnetic film areantiferromagnetically exchange-coupled with each other through thesecond nonmagnetic film.

[0063] In one embodiment of the invention, at least one of the firstferromagnetic film and the second ferromagnetic film has a magnetizationdirection in a planar direction thereof.

[0064] In one embodiment of the invention, the third ferromagnetic filmand the fourth ferromagnetic film have different strengths of saturatedmagnetization from each other.

[0065] In one embodiment of the invention, the third ferromagnetic filmand the fourth ferromagnetic film have different thicknesses from eachother.

[0066] In one embodiment of the invention, the third ferromagnetic filmand the fourth ferromagnetic film are magnetization-rotated while beingkept anti-parallel to each other.

[0067] In one embodiment of the invention, the second ferromagnetic filmincludes a third nonmagnetic film, a fifth ferromagnetic film, and asixth ferromagnetic film. The fifth ferromagnetic film and the sixthferromagnetic film are antiferromagnetically exchange-coupled with eachother through the third nonmagnetic film.

[0068] In one embodiment of the invention, the first nonmagnetic film isan insulating film.

[0069] According to still another aspect of the invention, amagneto-resistive effect memory cell includes a first ferromagneticfilm; a second ferromagnetic film; a first nonmagnetic film interposedbetween the first ferromagnetic film and the second ferromagnetic film;and at least one conductive film for causing a magnetization rotation ofat least the first ferromagnetic film. The first ferromagnetic film hasa magnetization more easily rotatable the a magnetization of the secondferromagnetic film by an external magnetic field. The firstferromagnetic film includes an amorphous magnetic film, and a thirdnonmagnetic film in contact with the first nonmagnetic film andinterposed between the amorphous film and the first nonmagnetic film.

[0070] In one embodiment of the invention, at least one of the firstferromagnetic film and the second ferromagnetic film has a magnetizationdirection in a planar direction thereof.

[0071] In one embodiment of the invention, the first nonmagnetic film isan insulating film.

[0072] In one embodiment of the invention, at least two layer structuresare provided, each layer structure including the first ferromagneticfilm, the second ferromagnetic film, and the first nonmagnetic filminterposed between the first ferromagnetic film and the secondferromagnetic film. The at least two layer structures are stacked withat least one second nonmagnetic film interposed therebetween.

[0073] In one embodiment of the invention, the second ferromagneticfilms of the at least two layer structures have different magneticcoercive forces from each other.

[0074] According to still another aspect of the invention, an MRAMincludes a plurality of the above-described magneto-resistive effectmemory cells. The plurality of conductive films are arranged in at leastone prescribed direction.

[0075] According to still another aspect of the invention, amagneto-resistive effect memory cell includes a first ferromagneticfilm; a second ferromagnetic film; a first nonmagnetic film interposedbetween the first ferromagnetic film and the second ferromagnetic film;and at least one conductive film for causing a magnetization rotation ofat least the first ferromagnetic film. The first ferromagnetic film hasa magnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field. The firstferromagnetic film includes a second nonmagnetic film, a thirdferromagnetic film, and a fourth ferromagnetic film. The thirdferromagnetic film and the fourth ferromagnetic film areantiferromagnetically exchange-coupled with each other through thesecond nonmagnetic film.

[0076] In one embodiment of the invention, a magneto-resistive effectmemory cell at least one of the first ferromagnetic film and the secondferromagnetic film has a magnetization direction in a planar directionthereof.

[0077] In one embodiment of the invention, the third ferromagnetic filmand the fourth ferromagnetic film have different strengths of saturatedmagnetization from each other.

[0078] In one embodiment of the invention, the third ferromagnetic filmand the fourth ferromagnetic film have different thicknesses from eachother.

[0079] In one embodiment of the invention, the third ferromagnetic filmand the fourth ferromagnetic film are magnetization-rotated while beingkept anti-parallel to each other.

[0080] In one embodiment of the invention, the second ferromagnetic filmincludes a third nonmagnetic film, a fifth ferromagnetic film, and asixth ferromagnetic film. The fifth ferromagnetic film and the sixthferromagnetic film are antiferromagnetically exchange-coupled with eachother through the third nonmagnetic film.

[0081] In one embodiment of the invention, the first nonmagnetic film isan insulating film.

[0082] In one embodiment of the invention, at least two layer structuresare provided, each layer structure including the first ferromagneticfilm, the second ferromagnetic film, and the first nonmagnetic filminterposed between the first ferromagnetic film and the secondferromagnetic film. The at least two layer structures are stacked withat least one fourth nonmagnetic film interposed therebetween.

[0083] In one embodiment of the invention, the second ferromagneticfilms of the at least two layer structures have different magneticcoercive forces from each other.

[0084] According to still another aspect of the invention, an MRAMincludes a plurality of the above-described magneto-resistive effectmemory cells. The plurality of conductive films are arranged in at leastone prescribed direction.

[0085] According to still another aspect of the invention, a method forwriting information to and reading information from a magneto-resistiveeffect memory cell is provided. The magneto-resistive effect memory cellincludes a first ferromagnetic film, a second ferromagnetic film, anonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film, and at least one conductive film. The firstferromagnetic film has a magnetization more easily rotatable than amagnetization of the second ferromagnetic film by an external magneticfield. The method includes the steps of causing a first current to flowin the at least one conductive film to cause a magnetization rotation ofat least the first ferromagnetic film, thereby writing information inthe magneto-resistive effect memory cell; and causing a second currentto flow in the first ferromagnetic film, the nonmagnetic film, and thesecond ferromagnetic film, and causing a third current, which is acombination of a positive bias current and a negative bias current, toflow in the at least one conductive film, thereby reading a voltagevalue corresponding to the second current and thus reading informationwritten in the magneto-resistive element memory cell.

[0086] In one embodiment of the invention, the third current has a levelwhich causes a magnetization rotation of the first ferromagnetic filmbut does not cause a magnetization rotation of the second ferromagneticfilm.

[0087] According to still anther aspect of the invention, a method forwriting information to and reading information from an MRAM including aplurality of magneto-resistive effect memory cells is provided. Eachmagneto-resistive effect memory cell includes a first ferromagneticfilm, a second ferromagnetic film, a nonmagnetic film interposed betweenthe first ferromagnetic film and the second ferromagnetic film, and atleast one conductive film. The first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field. The plurality ofconductive films are arranged in at least one prescribed direction. Themethod includes the steps of causing a first current to flow in the atleast one conductive film of a first magneto-resistive effect memorycell of the plurality of magneto-resistive effect memory cells to causea magnetization rotation of at least the first ferromagnetic film of thefirst magneto-resistive effect memory cell, thereby writing informationin the first magneto-resistive effect memory cell; and causing a secondcurrent to flow in the first ferromagnetic film, the nonmagnetic film,and the second ferromagnetic film of the first magneto-resistive effectmemory cell, and causing a third current, which is a combination of apositive bias current and a negative bias current, to flow in the atleast one conductive film of the first magneto-resistive effect memorycell, thereby reading a voltage value corresponding to the secondcurrent and thus reading information written in the firstmagneto-resistive effect memory cell.

[0088] In one embodiment of the invention, the third current has a levelwhich causes a magnetization rotation of the first ferromagnetic filmbut does not cause a magnetization rotation of the second ferromagneticfilm.

[0089] In one embodiment of the invention, the method further includesthe step of causing a fourth current to flow in the at least oneconductive film of a second magneto-resistive effect memory cell otherthan the first magneto-resistive effect memory cell, the fourth currentflowing in a direction for canceling a magnetic field leaked to a thirdmagneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.

[0090] In one embodiment of the invention, the second magneto-resistiveeffect memory cell is identical with the third magneto-resistive effectmemory cell.

[0091] According to still another aspect of the invention, a method forreading information from a magneto-resistive effect memory cell isprovided. The magneto-resistive effect memory cell includes a firstferromagnetic film, a second ferromagnetic film, a nonmagnetic filminterposed between the first ferromagnetic film and the secondferromagnetic film, and at least one conductive film. The firstferromagnetic film has a magnetization more easily rotatable than amagnetization of the second ferromagnetic film by an external magneticfield. The method includes the step of causing a first current to flowin the first ferromagnetic film, the nonmagnetic film, and the secondferromagnetic film, and causing a second current, which is a combinationof a positive bias current and a negative bias current, to flow in theat least one conductive film, thereby reading a voltage valuecorresponding to the first current and thus reading information writtenin the magneto-resistive effect memory cell.

[0092] In one embodiment of the invention, the second current has alevel which causes a magnetization rotation of the first ferromagneticfilm but does not cause a magnetization rotation of the secondferromagnetic film.

[0093] According to still another aspect of the invention, a method forreading information from an MRAM including a plurality ofmagneto-resistive effect memory cells is provided. Eachmagneto-resistive effect memory cell includes a first ferromagneticfilm, a second ferromagnetic film, a nonmagnetic film interposed betweenthe first ferromagnetic film and the second ferromagnetic film, and atleast one conductive film. The first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field. The plurality ofconductive films are arranged in at-least one prescribed direction. Themethod includes the step of causing a first current to flow in the firstferromagnetic film, the nonmagnetic film, and the second ferromagneticfilm of a first magneto-resistive effect memory cell of the plurality ofmagneto-resistive effect memory cells, and causing a second current,which is a combination of a positive bias current and a negative biascurrent, to flow in the at least one conductive film of the firstmagneto-resistive effect memory cell, thereby reading a voltage valuecorresponding to the first current and thus reading information writtenin the first magneto-resistive effect memory cell.

[0094] In one embodiment of the invention, the second current has alevel which causes a magnetization rotation of the first ferromagneticfilm but does not cause a magnetization rotation of the secondferromagnetic film.

[0095] In one embodiment of the invention, the method further includesthe step of causing a third current to flow in the at least oneconductive film of a second magneto-resistive effect memory cell otherthan the first magneto-resistive effect memory cell, the third currentflowing in a direction for canceling a magnetic field leaked to a thirdmagneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.

[0096] In one embodiment of the invention, the second magneto-resistiveeffect memory cell is identical with the third magneto-resistive effectmemory cell.

[0097] According to still another aspect of the invention, a method forwriting multiple levels of a signal to and reading multiple levels of asignal from a magneto-resistive effect memory cell is provided. Themagneto-resistive effect memory cell includes at least two layerstructures; at least one first nonmagnetic film interposed between theat least two layer structures; and at least one conductive film. Each ofthe at least two layer structures includes a first ferromagnetic film, asecond ferromagnetic film, and a second nonmagnetic film interposedbetween the first ferromagnetic film and the second ferromagnetic film.The first ferromagnetic film has a magnetization more easily rotatablethan a magnetization of the second ferromagnetic film. The methodincludes the steps of causing a first current in the at least oneconductive film to cause a magnetization rotation of at least one of thefirst ferromagnetic film and the second ferromagnetic film of each ofthe at least two layer structures, or to cause a magnetization rotationof none of the first ferromagnetic film and the second ferromagneticfilm of each of the at least two layer structures, thereby writingmultiple levels of a signal in the magneto-resistive effect memory cell;and causing a second current to each of the at least two layerstructures to compare a resistance value corresponding to the secondcurrent and a reference resistance value, thereby reading the multiplelevels of the signal written in the magneto-resistive effect memorycell.

[0098] In one embodiment of the invention, the method further includesthe step of causing a current which rises in a gradually increasingmanner to flow in the at least one conductive film.

[0099] According to still another aspect of the invention, a method forwriting multiple levels of a signal to a magneto-resistive effect memorycell is provided. The magneto-resistive effect memory cell includes atleast two layer structures; at least one first nonmagnetic filminterposed between the at least two layer structures; and at least oneconductive film. Each of the at least two layer structures includes afirst ferromagnetic film, a second ferromagnetic film, and a secondnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film. The first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film. The method includes the steps of causing a firstcurrent to flow in the at least one conductive film to cause amagnetization rotation of at least one of the first ferromagnetic filmand the second ferromagnetic film of each of the at least two layerstructures, or to cause a magnetization rotation of none of the firstferromagnetic film and the second ferromagnetic film of each of the atleast two layer structures, thereby writing multiple levels of a signalin the magneto-resistive effect memory cell.

[0100] According to still another aspect of the invention, a method forreading multiple levels of a signal from a magneto-resistive effectmemory cell is provided. The magneto-resistive effect memory cellincludes at least two layer structures; at least one first nonmagneticfilm interposed between the at least two layer structures: and at leastone conductive film. Each of the at least two layer structures includesa first ferromagnetic film, a second ferromagnetic film, and a secondnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film. The first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film. The method includes the steps of causing a firstcurrent to flow in each of the at least two layer structures to comparea resistance value corresponding to the first current and a referenceresistance value, thereby reading multiple levels of a signal written inthe magneto-resistive effect memory cell.

[0101] In one embodiment of the invention, the method further includesthe step of causing a current which rises in a gradually increasingmanner to flow in the at least one conductive film.

[0102] According to still another aspect of the invention, a method forwriting multiple levels of a signal to and reading multiple levels of asignal from an MRAM including a plurality of magneto-resistive effectmemory cells is provided. Each magneto-resistive effect memory cellincludes at least two layer structures; at least one first nonmagneticfilm interposed between the at least two layer structures; and at leastone conductive film. Each of the at least two layer structures includesa first ferromagnetic film, a second ferromagnetic film, and a secondnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film. The first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film. The plurality of conductive films are arranged in atleast one prescribed direction. The method includes the steps of causinga first current to flow in the at least one conductive film of a firstmagneto-resistive effect memory cell of the plurality ofmagneto-resistive effect memory cells to cause a magnetization rotationof at least one of the first ferromagnetic film and the secondferromagnetic film of each of the at least two layer structures of thefirst magneto-resistive effect memory cell, or to cause a magnetizationrotation of none of the first ferromagnetic film and the secondferromagnetic film of each of the at least two layer structures of thefirst magneto-resistive effect memory cell, thereby writing multiplelevels of a signal in the first magneto-resistive effect memory cell;and causing a second current to flow in each of the at least two layerstructures of the first magneto-resistive effect memory cell to comparea resistance value corresponding to the second current and a referenceresistance value, thereby reading the multiple levels of the signalwritten in the first magneto-resistive effect memory cell.

[0103] In one embodiment of the invention, the method further includesthe step of causing a current which rises in a gradually increasingmanner to flow in the at least one conductive film.

[0104] In one embodiment of the invention, the method further includesthe step of causing a third current to flow in the at least oneconductive film of a second magneto-resistive effect memory cell otherthan the first magneto-resistive effect memory cell, the third currentflowing in a direction for canceling a magnetic field leaked to a thirdmagneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.

[0105] In one embodiment of the invention, the second magneto-resistiveeffect memory cell is identical with the third magneto-resistive effectmemory cell.

[0106] According to still another aspect of the invention, a method forwriting multiple levels of a signal in an MRAM including a plurality ofmagneto-resistive effect memory cells is provided. Eachmagneto-resistive effect memory cell includes at least two layerstructures; at least one first nonmagnetic film interposed between theat least two layer structures; and at least one conductive film. Each ofthe at least two layer structures includes a first ferromagnetic film, asecond ferromagnetic film, and a second nonmagnetic film interposedbetween the first ferromagnetic film and the second ferromagnetic film.The first ferromagnetic film has a magnetization more easily rotatablethan a magnetization of the second ferromagnetic film. The plurality ofconductive films are arranged in at least one prescribed direction. Themethod includes the steps of causing a first current of flow in the atleast one conductive film of a first magneto-resistive effect memorycell of the plurality of magneto-resistive effect memory cells to causea magnetization rotation of at least one of the first ferromagnetic filmand the second ferromagnetic film of each of the at least two layerstructures of the first magneto-resistive effect memory cell, or tocause a magnetization rotation of none of the first ferromagnetic filmand the second ferromagnetic film of each of the at least two layerstructures of the first magneto-resistive effect memory cell, therebywriting multiple levels of a signal in the first magneto-resistiveeffect memory cell.

[0107] In one embodiment of the invention, the method further includesthe step of causing a second current to flow in the at least oneconductive film of a second magneto-resistive effect memory cell otherthan the first magneto-resistive effect memory cell, the second currentflowing in a direction for canceling a magnetic field leaked to a thirdmagneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.

[0108] In one embodiment of the invention, the second magneto-resistiveeffect memory cell is identical with the third magneto-resistive effectmemory cell.

[0109] According to still another aspect of the invention, a method forreading multiple levels of a signal from an MRAM including a pluralityof magneto-resistive effect memory cells is provided. Eachmagneto-resistive effect memory cell includes at least two layerstructures; at least one first nonmagnetic film interposed between theat least two layer structures; and at least one conductive film. Each ofthe at least two layer structures includes a first ferromagnetic film, asecond ferromagnetic film, and a second nonmagnetic film interposedbetween the first ferromagnetic film and the second ferromagnetic film.The first ferromagnetic film has a magnetization more easily rotatablethan a magnetization of the second ferromagnetic film. The plurality ofconductive films are arranged in at least one prescribed direction. Themethod includes the steps of causing a first current to flow in each ofthe at least two layer structures of a first magneto-resistive effectmemory cell of the plurality of magneto-resistive effect memory cells tocompare a resistance value corresponding to a the first current and areference resistance value, thereby reading multiple levels of a signalwritten in the first magneto-resistive effect memory cell.

[0110] In one embodiment of the invention, the method further includesthe step of causing a current which rises in a gradually increasingmanner to flow in the at least one conductive film.

[0111] In one embodiment of the invention, the method further includesthe step of causing a second current to flow in the at least oneconductive film of a second magneto-resistive effect memory cell otherthan the first magneto-resistive effect memory cell, the second currentflowing in a direction for canceling a magnetic field leaked to a thirdmagneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.

[0112] In one embodiment of the invention, the second magneto-resistiveeffect memory cell is identical with the third magneto-resistive effectmemory cell.

[0113] According to one aspect of the present invention, a free layer inwhich the magnetization direction is relatively easily rotatable by theexternal magnetic field includes a ferromagnetic film having a smallmagnetic coercive force even though being thin, and an amorphous film.

[0114] According to another aspect of the present invention, a freelayer includes a synthesized ferrimagnetic film including ferromagneticfilms which are antiferromagnetically exchange-coupled to each other.

[0115] Thus, the invention described herein makes possible theadvantages of providing a microscopic magnetic magneto-resistive effectelement and a microscopic magneto-resistive effect memory cell whichinclude a ferromagnetic film and are sufficiently easily operable as aresult of the strength of the anti-magnetic component of theferromagnetic film being reduced, an MRAM including a plurality of suchmagneto-resistive effect elements or a plurality of magneto-resistiveeffect memory cells integrated at a high density, and a method forperforming information write or read to or from the microscopicmagneto-resistive effect memory cell.

[0116] These and other advantages of the present invention will becomeapparent to those skilled in the art upon reading and understanding thefollowing detailed description with reference to the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0117]FIG. 1 is a cross-sectional view of an MR effect memory cell in afirst example according to the present invention;

[0118]FIGS. 2A and 2B are diagrams illustrating an operation principleof the MR effect memory cell in the first example;

[0119]FIG. 3 is a cross-sectional view of an MR effect memory cell in asecond example according to the present invention;

[0120]FIGS. 4A through 4C are diagrams illustrating an operationprinciple of the MR effect memory cell in the second example;

[0121]FIG. 5A is a plan view of an MRAM in a third example according tothe present invention;

[0122]FIG. 5B is a partial isometric view of the MRAM shown in FIG. 5A;

[0123]FIG. 5C is an exemplary partial cross-sectional view of the MRAMshown in FIG. 5A;

[0124]FIG. 6A is a cross-sectional view of an MR effect memory cell inthe third example;

[0125]FIG. 6B is a plan view of the MR effect memory cell in the thirdexample;

[0126]FIGS. 7A through 7D are cross-sectional views of an MR effectmemory cell in a fourth example according to the present invention;

[0127]FIGS. 8A through 8D are cross-sectional views of a MR portion in afifth example according to the present invention;

[0128]FIGS. 8E through 8G are isometric views of ferromagnetic films ina soft magnetic film of an MR portion in the fifth example according tothe present invention;

[0129]FIGS. 9A and 9B are graphs illustrating an operation of an MReffect memory cell in a sixth example according to the presentinvention;

[0130]FIGS. 10A and 10B are graphs illustrating an operation of an MReffect memory cell in a seventh example according to the presentinvention;

[0131]FIGS. 11A and 11B are graphs illustrating an operation of an MReffect memory cell in a ninth example according to the presentinvention;

[0132]FIG. 12A is a configuration diagram of an MRAM in a fourteenthexample according to the present invention;

[0133]FIG. 12B is a partial isometric view of the MRAM shown in FIG.12A;

[0134]FIGS. 12C, 12D and 12E are exemplary partial isometric views ofthe MRAM shown in FIG. 12A;

[0135]FIG. 12F is a plan view of the MRAM shown in Figure in 12A;

[0136]FIG. 13 is a graph illustrating an operation of an MR effectmemory cell in a twentieth example according to the present invention;

[0137]FIG. 14 is an asteroid-type magnetic field curve of the MR effectmemory cell in the twentieth example;

[0138]FIG. 15A is a configuration diagram of an MRAM in the twentiethexample;

[0139]FIG. 15B is a plan view of the MRAM in the twentieth example;

[0140]FIG. 16A is a partial isometric view of an MR effect head in atwenty-first example according to the present invention:

[0141]FIG. 16B is a cross-sectional view of the MR effect head shown inFIG. 16A;

[0142]FIG. 17A is a plan view of a magnetic disk apparatus in thetwenty-first example; and

[0143]FIG. 17B is a cross-sectional view of the magnetic disk apparatusshown in FIG. 17A.

DESCRIPTION OF THE EMBODIMENTS

[0144] Hereinafter, the present invention will be described by way ofillustrative examples with reference to the accompanying drawings.

EXAMPLE 1

[0145]FIG. 1 shows a cross-sectional view of an MR effect memory cell1000 in a first example according to the present invention.

[0146] The MR effect memory cell 1000 is a spin valve-type MR effectmemory cell using a hard magnetic film (hereinafter, referred to as an“HM spin valve-type MR effect memory cell”).

[0147] The MR effect memory cell 1000 includes a MR portion 100,conductive films 140, 150 and 170, and an insulating film 160. Theconductive films 140 and 150 respectively act as a part of a sense lineand a bit line, or vice versa when the MR effect memory cell 1000 isincorporated into an MRAM. The conductive film 170 acts as a part of aword line when the MR effect memory cell 1000 is incorporated into anMRAM. The MR portion 100 includes a hard magnetic film 110 (secondferromagnetic film) a nonmagnetic insulating film 120, and a softmagnetic film 130 (first ferromagnetic film). The soft magnetic film 130is more easily magnetization-rotated than the hard magnetic film 110 byan external magnetic field. The MR portion 100 is electrically connectedwith the conductive films 140 and 150. The conductive film 170 isprovided above the MR portion 100 with the insulating film 160interposed therebetween.

[0148] In the drawings attached to this specification, the arrows shownin magnetic films represent the directions of the magnetization of therespective magnetic films. It should be noted that the magnetizationdirection of each magnetic film is not limited to the magnetizationdirection shown in the drawings and is variable in various examples. Themagnetization direction can also be changed by a writing operation and areading operation.

[0149] The MR effect memory cell 1000 operates as follows. Informationis written by causing magnetization inversion of the hard magnetic film110 by a magnetic field generated by a current which flows in theconductive film 170 (word line). Information is read by causingmagnetization inversion of the soft magnetic film 130 without causingmagnetization inversion of the hard magnetic film 110. A magnetic fieldcan be generated by causing a current to flow in the conductive film 140or 150 which acts as the sense line in addition to the conductive film170. In this case, it is preferable that the sense line formed of aplurality of conductive films 140 or conductive films 150 and the wordlines formed of a plurality of conductive films 170 are perpendicular toeach other.

[0150] Such an information write and read operation realizes anon-destructive read out (NDRO) of the MR effect memory cell 1000. Inthis case, magnetization inversion requires two magnetic field strengththreshold values, i.e., a writing threshold value Hh and a readingthreshold value Hs which respectively correspond to a magnetic coerciveforce of the hard magnetic film 110 and a magnetic coercive force of asoft magnetic film 130.

[0151]FIGS. 2A and 2B show an operation principle of the MR effectmemory cell 1000. A signal or data is written in the MR effect memorycell 1000 as follows. A positive pulse current 501 or a negative pulsecurrent 502 is caused to flow in the conductive film 170 to apply amagnetic field which exceeds the writing threshold value Hhcorresponding to the magnetic coercive force of the hard magnetic film110 to the hard magnetic film 110, thus causing magnetization inversionof the hard magnetic film 110. The level of the signal, i.e., “1” or “0”is written corresponding to the magnetization direction of the hardmagnetic film 110.

[0152] The written signal or data is read as follows. While a constantcurrent flows in the conductive films 140 and 150 (FIG. 1), a weak pulsecurrent is caused to flow in the conductive film 170, thus generating amagnetic field having a strength which is equal to or more than thethreshold value Hs corresponding to the magnetic coercive force of thesoft magnetic film 130 and is equal to or less than the threshold valueHh corresponding to the magnetic coercive force of the hard magneticfilm 110. The signal is read by determining whether the magnetizationinversion of the soft magnetic film 130 is caused or not. Specifically,the level of the signal, i.e., the data storage state is identified tobe “1” or “0” by monitoring a change in the resistance value of the MRportion 100 through the conductive films 140 and 150.

[0153] When a current similar to the positive pulse current 501 iscaused to flow in the conductive film 170 while the MR effect memorycell 1000 is in the data storage state of “1” (FIG. 2A), the resistancevalue of the MR portion 100 is not changed. When a current similar tothe positive pulse current 501 is caused to flow in the conductive film170 while the MR effect memory cell 1000 is in the data storage state of“0” (FIG. 2A), the resistance value of the MR portion 100 increases.When a current similar to the negative pulse current 502 is caused toflow in the conductive film 170, the result is opposite to the above.

[0154] When a pulse current 503 having a combination of positive andnegative pulses is caused to flow in the conductive film 170 while theMR effect memory cell 1000 is in the data storage state of “1”, theresistance value of the MR portion 100 changes from 0 to a positivevalue. Thus, the change ratio (ΔR₁/Δt) is positive. By contrast, whenthe pulse current 503 is caused to flow in the conductive film 170 whilethe MR effect memory cell 1000 is in the data storage state of “0”, thechange ratio (ΔR₁/Δt) is negative. It should be noted that the pulsecurrent 503 has a level which does not cause magnetization inversion ofthe hard magnetic film 110 but can cause magnetization inversion of thesoft magnetic film 130.

[0155] The above-described operation principle allows a signal to beread from the MR effect memory cell 1000. In an HM spin valve-type MReffect memory cell such as the MR effect memory cell 1000, themagnetization state of the hard magnetic film 110 does not change whilea signal is being read and thus an NDRO is possible.

[0156] A semi-hard magnetic film is usable instead of the hard magneticfilm 110.

[0157] The hard magnetic film 110 and the soft magnetic film 130 can belocated opposite of each other.

[0158] Especially when the conductive film 170 is used for applying amagnetic field to the MR portion 100, the soft magnetic film 130 ispreferably located as close as possible to the conductive film 170.

[0159] Herein, an example of a so-called constant current mode isdescribed, in which a change in the resistance value occurring while aconstant current is applied is detected as a voltage change.Alternatively, a so-called constant voltage mode is usable, in which achange in the current level occurring while a constant voltage isapplied is detected as a current change.

[0160] The structure of the MR effect memory cell 1000 is usable as anMR effect element. The MR effect element is usable as a magnetic head,and a magnetic field applied from a recording medium or the like issensed by the MR portion 100. The conductive film 170 can be eliminatedwhen the MR effect element is used as a magnetic head.

EXAMPLE 2

[0161]FIG. 3 shows a cross-sectional view of an MR effect memory cell2000 in a second example according to the present invention. Throughoutthis specification, identical elements previously discussed with respectto figures bear identical reference numerals and the detaileddescriptions thereof will be omitted.

[0162] The MR effect memory cell 2000 is a spin valve-type MR effectmemory cell using an antiferromagnetic film (hereinafter, referred to asan “AF spin valve-type MR effect memory cell”).

[0163] The MR effect memory cell 2000 includes a MR portion 101,conductive films 141, 150 and 170, and an insulating film 160. Theconductive films 141 and 150 respectively act as a part of a sense lineand a bit line, or vice versa when the MR effect memory cell 2000 isincorporated into an MRAM. The conductive film 170 acts as a part of aword line when the MR effect memory cell 2000 is incorporated into anMRAM. The MR portion 101 includes an antiferromagnetic film 180, aferromagnetic film 190 (second ferromagnetic film) exchange-coupled withthe antiferromagnetic film 180, a nonmagnetic insulating film 120, and asoft magnetic film 130 (first ferromagnetic film). The MR portion 101 iselectrically connected with the conductive films 141 and 150. The softmagnetic film 130 is more easily magnetization-rotated than theferromagnetic film 190 by an external magnetic field.

[0164] A magnetic field generated by a current flowing in the conductivefilm 170 (word line) does not cause magnetization inversion in theferromagnetic film 190 but causes magnetization inversion only in thesoft magnetic film 130 which is magnetically separated from theferromagnetic film 190 by the nonmagnetic insulating film 120.Accordingly, information write and read is performed only bymagnetization inversion of the soft magnetic film 130. Therefore,although it is difficult to realize an NDRO, there is only one magneticfield threshold value required for causing magnetization inversion andthus the operation principle is simple.

[0165]FIGS. 4A and 4B show an operation principle of the MR effectmemory cell 2000.

[0166] The ferromagnetic film 190 is exchange-coupled with theantiferromagnetic 180, and the magnetization of the ferromagnetic film190 is pinned in one direction.

[0167] A signal or data is written in the MR effect memory cell 2000 asfollows. A positive pulse current 511 or a negative pulse current 512 iscaused to flow in the magnetic film 170 to apply a magnetic field whichis equal to or more than the reading threshold value Hs corresponding toa magnetic coercive force of the soft magnetic film 130 to the softmagnetic film 130, thus causing magnetization inversion of the softmagnetic film 130. The level of the signal, i.e., “1” or “0” is writtencorresponding to the magnetization direction of the soft magnetic film130.

[0168] The written signal or data is read as follows. While a constantcurrent flows in the conductive films 141 and 150 (FIG. 3), a positiveor negative weak pulse current is caused to flow in the conductive film170, thus generating a magnetic field having a strength which is equalto or more than the threshold value Hs corresponding to the magneticcoercive force of the soft magnetic film 130. The signal is read bydetermining whether the magnetization inversion of the soft magneticfilm 130 is caused or not. Specifically, the level of the signal, i.e.,the data storage state is identified to be “1” or “0” by monitoring achange in the resistance value of the MR portion 101 through theconductive films 141 and 150.

[0169] When a positive pulse current 513 is caused to flow in theconductive film 170 while the MR effect memory cell 2000 is in the datastorage state of “1” (FIG. 4B), the resistance of the MR portion 101 isnot changed (ΔR₂=0). When the positive pulse current 513 is caused toflow in the conductive film 170 while the MR effect memory device 2000is in the data storage state of “0” (FIG. 4B), the resistance of the MRportion 101 changes (ΔR₂≠0). When a negative pulse current (not shown)is caused to flow in the conductive film 170, the result is opposite tothe above. It should be noted that the pulse current 503 has a levelwhich does not cause magnetization inversion of the hard magnetic film110 but can cause magnetization inversion of the soft magnetic film 130.

[0170] The above-described operation principle allows a signal to beread from the MR effect memory cell 2000. In an AF spin valve-type MReffect memory cell such as the MR effect memory cell 2000, the signalwhich has been written is destroyed when the signal is read.Accordingly, an NDRO is difficult to be realized but not impossible. Amethod for realizing an NDRO will be described below with reference toFIG. 4C.

[0171] When a signal is read by a method of detecting a difference ΔR₃between the resistance value of the MR portion 101 and a referenceresistance value R₁, the state of the signal, i.e., “1” or “0 ” can beread without causing a pulse current to flow in the conductive film 170.Since the signal which is written is not destroyed when being read inthis case, an NDRO can be realized. The reference resistance value R₁preferably is a value in the variable range of values of the resistanceof the MR portion 101. When a plurality of MR effect memory cells areintegrated, a resistance value of one of the plurality of MR effectmemory cells is preferably used as the reference resistance value R₁.

[0172] As an antiferromagnetic film 180, a magnetization rotationprevention film is usable.

[0173] The ferromagnetic film 190 and the soft magnetic film 130 can belocated opposite of each other.

[0174] The structure of the MR effect memory cell 2000 is usable as anMR effect element as in the first example.

[0175] The hard magnetic film 110 of the MR effect memory cell 1000 inthe first example and the ferromagnetic film 190 of the MR effect memorycell 2000 in the second example correspond to a pinned layer of an MReffect element. Exemplary suitable metal and alloy materials used forthe hard magnetic film 110 and the ferromagnetic film 190 include Co,Co—Fe, Ni—Fe, and Ni—Fe—Co. Specifically, Co and a Co—Fe alloy aresuitable for obtaining a high MR ratio, and thus a Co-rich material ispreferably used for an interface between the hard magnetic film 110 orferromagnetic film 190 and the nonmagnetic insulating film 120.

[0176] XMnSb (X is preferably at least one element selected from thegroup consisting of Ni, Pt, Pd and Cu) has a sufficiently high magneticpolarization ratio and thus provides a sufficiently high MR ratio whenused in an MR effect element.

[0177] Exemplary suitable oxide magnetic materials used for the hardmagnetic film 110 and the ferromagnetic film 190 include MFe₂O₄ (M ispreferably at least one element selected from the group consisting ofFe, Co and Ni). MFe₂O₄ is ferromagnetic up to a relatively hightemperature. Co-rich or Ni-rich MFe₂O₄ has a higher resistance valuethan Fe-rich MFe₂O₄. Co-rich MFe₂O₄ has a relatively large magneticanisotropy. The hard magnetic film 110 and the ferromagnetic film 190having desirable characteristics can be obtained by adjusting thecomposition ratio of the components.

[0178] The hard magnetic film 110 and the ferromagnetic film 190preferably have a thickness of about 1 nm or more and about 10 nm orless.

[0179] A magnetization rotation prevention film used as theantiferromagnetic film 180 which is in contact with the ferromagneticfilm 190 can be formed of an irregular alloy such as, for example,Ir—Mn, Rh—Mn, Ru—Mn, or Cr—Pt—Mn. When the magnetization rotationprevention film is formed in a magnetic field, the magnetizationrotation prevention film can be exchange-coupled with the ferromagneticfilm 190, which simplifies the production process of the MR effectmemory cell 2000. Exemplary regular alloys usable for the magnetizationrotation prevention film include Ni—Mn and Pt—(Pd)—Mn. These regularalloys need to be heat-treated for regularization but have a sufficientlevel of stability against heat. Among the regular alloys, Pt—Mn isespecially preferable. Exemplary usable oxide materials include α-Fe₂O₃,NiO, or LTO₃ (L is a rare earth element excluding Ce, and T is Fe, Cr,Mn, or Co). When these materials having a relatively low level ofconductivity are used, the conductive film 141 is preferably located soas to be in direct contact with the ferromagnetic film 190 as shown inFIG. 3.

[0180] The soft magnetic film 130 of the MR effect memory cells 1000 and2000 in the first and second examples corresponds to a free layer of anMR effect element. Exemplary suitable materials for the soft magneticfilm 130 include Co, Co—Fe, Ni—Fe, and Ni—Fe—Co alloys. PreferableNi—Fe—Co alloys include Ni_(x)Fe_(y)Co_(z) (0.6≦×≦0.9, 0≦y≦0.3,0≦z≦0.4), which is Ni-rich; and Ni_(x′)Fe_(y′)Co_(z′) (0≦x′≦0.4,0≦y′≦0.5, 0.2≦z′≦0.95), which is Co-rich.

[0181] The alloys having the above-mentioned compositions have a lowmagnetic distortion (1×10⁵) which is required for sensors or MR heads.

EXAMPLES 3 through 20

[0182] In general, when the magnetization direction of a ferromagneticfilm is in a planar direction of the film, and w is the planar size ofthe film and d is the thickness of the film, the strength of ananti-magnetic field component inside the ferromagnetic film, which is inthe same direction as an external magnetic field component directed inthe planar direction of the ferromagnetic film, increases as d/wincreases. In other words, as the size of the MR effect element isreduced in accordance with an increase in the integration degree of anMRAM, the strength of the anti-magnetic field component of theferromagnetic film increases. Thus, a stronger magnetic field isrequired in order to magnetize the ferromagnetic film. A larger magneticcoercive force is required in order to stabilize the magnetized state.As a result, magnetization inversion by a magnetic field generated by acurrent flowing through a word line becomes more difficult.

[0183] As can be appreciated from the above, when the width of an MReffect element is as small as on the order of submicrometers, theanti-magnetic field component of the ferromagnetic film is notnegligible. Thus, a stronger magnetic field is required in order tomagnetize the ferromagnetic field.

[0184] According to the present invention, a free layer in which themagnetization direction is relatively easily rotatable by an applicationan external magnetic field includes a ferromagnetic film having a smallmagnetic coercive force even though being thin, and an amorphous film.Alternatively, a free layer includes a synthesized ferrimagnetic filmincluding ferromagnetic films which are antiferromagneticallyexchange-coupled to each other. By forming the free layer to have suchstructures, a microscopic MR effect memory cell or element can beprovided, and an MRAM including a plurality of such MR effect memorycells integrated at a high density can also be provided, as described inthe following examples.

EXAMPLE 3

[0185]FIG. 5A is a partial plan view of an MRAM 3000 in a third exampleaccording to the present invention, and FIG. 5B is a partial isometricview of the MRAM 3000.

[0186] The MRAM 3000 includes a plurality of MR effect memory cells 1000in the first example or a plurality of MR effect memory cells 2000 inthe second example which are arranged in a matrix. The MR effect memorycells 1000 and 2000 are CPPMR elements.

[0187] Herein, the MR portion 100 (or 101) has a shape of prism, but canhave a shape of circular cylinder, elliptical cylinder, truncated coneor truncated pyramid. A face of the MR portion 100 (or 101) which is incontact with the conductive films 140 or the like preferably has arelationship of L₁>W₁ where L₁ represents the width and W₁ represent thelength as shown in FIG. 5B in order to provide an anisotropy in shape.

[0188]FIG. 5C is a cross-sectional view illustrating a preferablecross-sectional shape of the conductive film 170 which is morepreferable for efficiently applying a magnetic field to the MR portion100 (or 101). Letters h and h′ each represent an angle made by a side ofthe cross-section facing the MR portion 100 (or 101) and another side.Preferably, at least one of angles h and h′ is an acute angle.

[0189] Due to the cross-sectional shape of the conductive film 170 asshown in FIG. 5C, the current flowing in the conductive film 170 at auniform density is caused to flow in the vicinity of the MR portion 100(or 101) in a larger amount than in the rest of the conductive film 170.Thus, the magnetic field can be efficiently applied to the MR portion100 (or 101). Such a cross-sectional shape is especially preferable whenthe aspect ratio (width/thickness) of the cross-section of theconductive film 170 is reduced due to the size reduction of the MRAM3000.

[0190] As can be appreciated from the above, the free layer in the MR100 (or 101) is preferably located as close as possible to theconductive film 170 in order to efficiently apply the magnetic field.Such an arrangement is preferable because it increases an operationmargin for selecting an MR portion in the MRAM 3000 even when asynthesized magnetic field generated by the conductive film 170 (wordline) and the sense line 150 (or 140) which are perpendicular to eachother is used. This occurs because the level of the current required forcausing a magnetization rotation is lowest at the operation point wherethe strength of the magnetic field generated by the conductive film 170(word line) and the strength of the magnetic field generated by thesense line 150 are equal to each other (i.e., when θ=45° in FIG. 14).

[0191] As shown in FIGS. 5A and 5B, in the MRAM 3000 including the CPPMRelements, the MR effect memory cells 1000 or 2000 are connected parallelto each other. Accordingly, even when the number N of the MR effectmemory cells increases, the S/N ratio is not substantially reduced.

[0192]FIG. 6A is a cross-sectional view of an MR effect memory cell 1001according to the present invention, and FIG. 6B is a plan view of anMRAM 3001 including a plurality of the MR effect memory cells 1001arranged in a matrix.

[0193] The MR effect memory cell 1001 includes a MR portion 102,conductive films 142, 143 and 171, and an insulating film 161. Theconductive films 142 and 143 respectively act as a part of a sense lineand a bit line, or vice versa when the MR effect memory cell 1001 isincorporated into an MRAM. The conductive film 171 acts as a part of aword line when the MR effect memory cell 1001 is incorporated into anMRAM. The MR portion 102 includes a hard magnetic film 111, anonmagnetic film 121, and a soft magnetic film 131. The MR portion 102is electrically connected with the conductive films 142 and 143. Theconductive film 171 is provided above the MR portion 102 with theinsulating film 161 interposed therebetween. The MR effect memory cell1001 having the above-described structure is a CIPMR element.

[0194] As shown in FIG. 6B, the MR effect memory cells 1001 areconnected in series. In such a case, when the number N of the MR effectmemory cells 1001 increases, the S/N ratio of the entirety of the MRAM3001 is considered to be reduced although the MR ratio of each MR effectmemory cell 1001 remains the same.

[0195] In some of the figures in the present application, includingFIGS. 5A and 6B, the MR portion is represented as being larger than thesense, word and other lines. This is merely for clarity, and the sizerelationship between the MR portion and the lines is not limited tothis. In order to efficiently apply a magnetic field to the MR portion,each line preferably covers the MR portions.

[0196] The MRAMs 3000 and 3001 are memory devices using a magneticproperty, and thus are nonvolatile unlike semiconductor DRAMs utilizingaccumulation of charges. Unlike semiconductor flash memory devices,there is no limit in the number of times of write/read operations inprinciple, and a time period required for write and erase operations isas short as on the order of nanoseconds.

[0197] The operation principle of each MR effect memory cell is asdescribed in the first and second examples. For producing the MRAM 3000or 3001, a plurality of MR effect memory cells 1000, 1001 or 2000 areprovided in a matrix. Specifically, a plurality of word lines are firstprovided in a lattice, and then the MR effect memory cells 1000, 1001 or2000 are provided respectively adjacent to intersections of the wordlines. In FIGS. 5A, 5B and 6B, the word lines (conductive film 170 or171) are shown in only one direction (i.e., row direction or columndirection) for simplicity and in conformity to FIGS. 1, 3 and 6A. Thelattice arrangement of the word lines will be described in detail in thefollowing examples.

[0198] A magnetic field generated by two intersecting word linesadjacent to a selected MR portion at address (N, M) is applied to theselected MR portion. One of the two word lines can be replaced with onesense line.

[0199] In an MRAM including a plurality of MR effect memory cells 1000shown in FIG. 1, when a synthesized magnetic field generated by the twoword lines exceeds the value of a switching magnetic field representedby an asteroid-type curve of the hard magnetic film 110, information iswritten. When the above-mentioned synthesized magnetic field does notexceed the value of the switching magnetic field but exceeds the valueof a switching magnetic field of the soft magnetic film 130, an NDRO ofinformation is performed from a desired MR effect memory cell 1000.

[0200] In an MRAM including a plurality of MR effect memory cells 2000shown in FIG. 3, the operation is basically the same as that of the MRAMincluding MR effect memory cells 1000 in that a synthesized magneticfield causes magnetization inversion of the soft magnetic film 130.

[0201] Information stored in these MRAMs can be read in the followingmanner. A pulse current is caused to flow in two word lines adjacent toa MR portion at address (N, M), and information stored in the MR portionis read based on a change in the resistance value which is monitoredthrough the sense line and the bit line connected to the MR portion.

[0202] As described with reference to FIG. 4C in the second example, anNDRO of the information stored in the MR portion at address (N, M) isrealized by comparing the resistance value of the MR portion and areference resistance value.

[0203] Alternatively, each word line and each sense line can be providedwith a switching device such as, for example, a transistor. An MRportion at address (N, M) can be selected by selecting the word line ofrow N and the sense line (or bit line) of column M by an addressdesignating signal. In order to prevent an inflow of a signal pulsethrough another path and a return of a harmonic component caused by anincrease in speed of signal pulse transfer and thus to transfer thesignal pulse efficiently, each MR portion is preferably provided with adiode or a transistor. Especially in order to deal with a high speedpulse response, a MOS transistor is preferably used.

[0204] As the MR effect memory cells are integrated at a higher density,the problem of leakage of a magnetic field generated by word lines to anarea other than the selected MR portion becomes more serious. In orderto alleviate an interference effect on the area other than the selectedMR portion caused by the leaked magnetic field, a pulse current ispreferably caused to flow not only in a pair of word lines generating amagnetic field in the MR portion at address (N, M) but also in at leastone more pair of word lines in the vicinity of or interposing theabove-mentioned MR portion. In this manner, the magnetic field leaked toanother MR portion, other than the MR portion at address (N, M), can becancelled by a magnetic field generated by word lines corresponding tothe another MR portion or by a magnetic field generated by word linescorresponding to still another MR portion. Thus, influence of the leakedmagnetic fields is reduced.

EXAMPLE 4

[0205]FIGS. 7A through 7D are cross-sectional views of an MR effectmemory cell 4000 in a fourth example according to the present invention.

[0206] The MR effect memory cell 4000 includes a MR portion 200, aninsulating film 162, and a conductive film 172. The MR portion 200includes hard magnetic films 112, 113 and 114, soft magnetic films 132,133 and 134, nonmagnetic insulating films 122, 123 and 124, andnonmagnetic films 222 and 223. The conductive film 172, which acts as apart of a word line when the MR effect memory cell 4000 is incorporatedin an MRAM, is provided above the MR portion 200 with the insulatingfilm 162 interposed therebetween.

[0207] The MR portion 200 includes a plurality of soft magneticfilm/nonmagnetic insulating film/hard magnetic film structures stackedwith a nonmagnetic film interposed between each structure of theplurality. In the MR portion 200 shown in FIG. 7A through 7D, three suchstructures are stacked. The number of such structures is optional.

[0208] In the fourth example, the hard magnetic films 112, 113 and 114have different magnetic coercive forces, and as a result, there are aplurality of magnetic field threshold values for writing. Accordingly,four different levels of a signal can be stored in one MR effect memorycell 4000. The magnetic coercive force of each of the hard magneticfilms 112, 113 and 114 can be changed by changing the composition or thethickness of the respective film. By a method of detecting a differenceΔR₄ between the resistance value of the MR portion 200 and a referenceresistance value R₂, the four levels of the signal stored (e.g., “0”,“1”, “2” and “3”) can be read.

[0209] Since the MR effect memory cell 4000 includes three soft magneticfilm/nonmagnetic insulating film/hard magnetic film structures, thereare four patterns of magnetization directions as shown in FIGS. 7Athrough 7D. Accordingly, four levels (e.g., “0”, “1”, “2” and “3”) can—be stored in one MR effect memory cell 4000.

[0210] Information is written in the MR effect memory cell 4000 bycausing magnetization inversion of the hard magnetic films 112, 113 and114 by a magnetic field which is generated by pulse currents 521, 522and 523 flowing in the conductive film 172. In the fourth example, themagnetic coercive force of the hard magnetic film 112 is smallest andthe magnetic coercive force of the hard magnetic film 114 is largest. Byadjusting the level of the pulse current flowing in the conductive film172, the hard magnetic film or films in which magnetization inversion iscaused can be selected among the hard magnetic films 112, 113 and 114.In the fourth example, the level of the pulse current flowing in theconductive film 172 gradually increases from the state in FIG. 7B towardthe state in FIG. 7D. In FIG. 7A, the level of a pulse current 520flowing in the conductive film 172 is still lower than the level of apulse current 521 in FIG. 7B. In FIG. 7A, magnetization inversion occursin none of the hard magnetic films; and in FIG. 7D, magnetizationinversion occurs in all of the hard magnetic films 112, 113 and 114.

[0211] Information is read from the MR effect memory cell 4000 by amethod of detecting the difference ΔR₄ between the resistance value ofthe MR portion 200 and the reference resistance value R₂ as describedabove.

[0212] Information can also be read by causing a current to flow in theconductive film 172 and reading a change in the resistance value of theMR portion 200. In this case, the change in the resistance value of theMR portion 200 can be detected by, for example, a comparison with thereference resistance value R₂.

[0213] The soft magnetic films 132, 133 and 134 can have differentmagnetic coercive forces. In such a case, many levels of the signal canbe stored in one MR effect memory cell 4000 by precisely adjusting thelevel of the pulse current flowing in the conductive film 172 anddetermining the film or films in which magnetization inversion is to becaused and the film or films in which magnetization inversion is not tobe caused among the soft magnetic films 132, 133 and 134. These levelsof the signal are preferably read by a method of detecting thedifference ΔR₄ between the resistance value of the MR portion 200 andthe reference resistance value R₂ as described above.

[0214] Alternatively, the magnetization direction of all the hardmagnetic films 112, 113 and 114 can be pinned, in which case the levelsof the signal can be stored by causing the magnetization inversion onlyin an arbitrary one of the soft magnetic films 132, 133 and 134 asdescribed in the second example.

EXAMPLE 5

[0215] In a fifth example according to the present invention, the MRportion 100 (FIG. 1) will be described in more detail. FIGS. 8A through8D are cross-sectional views of various examples of the MR portion 100in the fifth example.

[0216] Referring to FIG. 8A, the soft magnetic film 130, which is a freelayer, includes an interface magnetic film 220 in contact with thenonmagnetic insulating film 120 and a nonmagnetic film 210 in order toincrease the MR ratio. The free layer needs to have a soft magneticproperty and thus can be formed of a Ni-rich material. In the example ofFIG. 8A, the interface magnetic film 220 is formed of a Co-richmaterial, and the nonmagnetic film 210 is formed of, for example, CoFeBor CoMnB. Due to such a structure, even when the soft magnetic film 130has a thickness of about 2 nm or less, a sufficiently high MR ratio canbe provided without spoiling the soft magnetic property. An MR effectmemory cell including such a free layer is satisfactorily stable againstheat. In other words, an MR effect memory cell including a free layerhaving a magnetic effective thickness of about 2 nm or less can berealized when the free layer (soft magnetic film 130) includes theinterface magnetic film 220 and the nonmagnetic film 210. The interfacemagnetic film can be formed of an alloy material containing at least oneelement of Co, Ni and Fe or Ni_(x)—Coy—Fe_(z) as a main component, where0≦x≦0.4, 0.2≦y≦0.95, 0≦z0.5.

[0217] When the interface magnetic film 220 is excessively thick, thesoft magnetic property is deteriorated and thus the MR ratio is reduced.In order to avoid this, the interface magnetic film 220 needs to have athickness of 2 nm or less, preferably about 1.2 nm or less. Theinterface magnetic film 220, however, needs to have a thickness of about0.2 nm or more, preferably about 0.8 nm or more, in order to effectivelyact. The interface magnetic film 220 is preferably formed of Co or aCo—Fe alloy having a sufficiently high concentration of Co.

[0218] Referring to FIG. 8B, the soft magnetic film (free layer) 130 ofthe MR portion 100 has an exchange-coupled ferrimagnetic film structure.The soft magnetic film 130 acting as an exchange-coupled ferrimagneticfilms includes two ferromagnetic films 230 and 250 and a nonmagneticfilm 240. The two ferromagnetic films 230 and 250 are exchange-coupledto each other through the nonmagnetic film 240. This exchange couplingcan be made antiferromagnetic by forming the nonmagnetic film 240 tohave an appropriate thickness (for example, when the nonmagnetic film240 is formed of Ru, the thickness of the nonmagnetic film 240 is about0.6 nm or more and about 0.8 nm or less). In the example of FIG. 8B, theferromagnetic films 230 and 250 have different thicknesses from eachother or have different strengths of saturated magnetization from eachother.

[0219] The-nonmagnetic film 240 is preferably formed of a nonmagneticmetal material which relatively easily causes exchange coupling betweenmagnetic films, for example, Cu, Ag or Au. In consideration of thestability against heat at the interface between the ferromagnetic film230 and the nonmagnetic film 240 and the interface between theferromagnetic film 250 and the nonmagnetic film 240, the nonmagneticfilm 240 is more preferably formed of, for example, Ru, Rh, Ir, or Re.Ru is especially preferable. The ferromagnetic films 230 and 250 arepreferably formed of a metal magnetic material containing at least oneof Ni, Co and Fe as a main component.

[0220] The strength of saturated magnetization of a ferromagnetic filmis determined by multiplying the magnitude of a magnetic moment,inherent to the material, determining the magnetization by the volume ofthe ferromagnetic film (corresponding to the number of magnetic momentsincluded in the ferromagnetic film). In the case of the structure shownin FIG. 8B, the exchange-coupled ferromagnetic films 230 and 250 have anequal size in the planar direction thereof. Accordingly, the strength ofthe saturated magnetization in the planar direction of each of theferromagnetic films 230 and 250 is determined by the magnitude of themagnetic moment inherent in the material thereof and the thicknessthereof. In the soft magnetic film (free layer) 130 having such anexchange-coupled ferrimagnetic film structure, the effective magneticthickness of the soft magnetic film 130 is substantially the differencein the thickness between the ferromagnetic films 230 and 250. By causingthe ferromagnetic films 230 and 250 to have a thickness difference, theferromagnetic films 230 and 250 have a magnetization difference.Reduction in the effective magnetic thickness of the soft magnetic film130 is effective in improving the sensitivity of the MR portion 100 anda device including the MR portion 100.

[0221] Especially in order to cause the ferromagnetic films 230 and 250to have a magnetization difference by having a thickness difference, thethickness difference between the ferromagnetic films 230 and 250 ispreferably about 2 nm or less. Since the effective magnetic thickness ofthe soft magnetic film 130 is substantially the difference in thethickness between the ferromagnetic films 230 and 250, the soft magneticfilm 130 is about 2 nm or less.

[0222] For causing magnetization inversion of the free layer in whichthe thickness difference between two ferromagnetic films is about 2 nmor less, a stronger external magnetic field is required as theanti-magnetic field component becomes stronger. In production of anMRAM, an external magnetic field is generated by word lines (or senselines) and is applied to the MR portions. Even when the word lines areformed of a low resistance copper (Cu), the maximum possible level ofcurrent which can flow in the word lines is about 50 MA/cm². Inconsideration of an operation margin in light of the operation stabilityof the MRAM, the thickness difference between the ferromagnetic filmsestimated based on the external magnetic field which can be generated ispreferably on the order of several nanometers or less. As a result oftests using the structure of FIG. 8B, it has been found that thedifference thickness between the ferromagnetic films 230 and 250 is mostpreferably about 2 nm or less. The effective magnetic thickness of thefree layer (soft magnetic film 130) is preferably about 0.2 nm or moresince, otherwise, the soft magnetic property of the free layer isdeteriorated.

[0223] The magnetization rotation of the soft magnetic film 130 ispreferably performed as a rotation of an effective magnetizationdirection caused by the magnetization direction difference between thetwo ferromagnetic films 230 and 250 while the magnetization directionsof the ferromagnetic films 230 and 250 are maintained anti-parallelagainst an application of an external magnetic field. The reason is thata magnetization rotation which destroys the anti-parallel state of themagnetization directions of the two ferromagnetic films by anapplication of an external magnetic field is not preferable because sucha magnetization rotation needs to overcome the exchange coupling of theferromagnetic films 230 and 250 and thus requires a stronger externalmagnetic field than the magnetization rotation performed whilemaintaining the anti-parallel state. As shown in FIG. 8D, it iseffective for a low magnetic field operation of an MR effect memory cellto cause a magnetization rotation while the magnetization vectors of theferromagnetic films 230 and 250 are maintained anti-parallel to eachother against an application of an external magnetic field.

[0224]FIG. 8D shows a change in the magnetization direction of theferromagnetic films 230 and 250 occurring when the direction of theexternal magnetic field changes from H₁ to H₂. FIGS. 8E, 8F and 8G areisometric views of the ferromagnetic films 230 and 250 in the softmagnetic film 130. As the direction of the external magnetic fieldchanges from H₁ to H₂, the magnetization directions of the ferromagneticfilms 230 and 250 change from the directions shown in FIG. 8E to FIG. 8Fand further to FIG. 8G. The magnetization rotation of the soft magneticfilm 130 is performed as a rotation of an effective magnetizationdirection caused by the magnetization direction difference between thetwo ferromagnetic films 230 and 250 while the magnetization directionsof the ferromagnetic films 230 and 250 are maintained anti-parallel. InFIGS. 8E, 8F and 8G, the other films or layers of the MR portion 100 arenot shown for the sake of simplicity.

[0225] As a RAM using an MR effect element such as an MRAM is reduced insize to a submicrometer order, the processing precision is lowered andalso the processed element itself is liable to be influenced by eachparticle of a magnetic film. As a result, it is difficult to divide themagnetic film of the element into magnetic domains. Forming a free layerhaving an exchange-coupled ferrimagnetic film structure as in FIG. 8B iseffective in dividing the free layer into magnetic domains.

[0226] The MR portion shown in FIG. 8B has a satisfactory level ofstability against heat by the combination of (i) the division of thefree layer into magnetic domains and (ii) the magnetic coupling of thetwo ferromagnetic films by an antiferromagnetic exchange couplingenergy.

[0227] The above-described exchange-coupled ferrimagnetic film structureis also usable for a hard magnetic film 110 which is a pinned layer, asshown in FIG. 8C. In FIG. 5C, the hard magnetic film 110 includesferromagnetic films 260 and 280 and a nonmagnetic film 270. Thenonmagnetic film 270 is preferably formed of a nonmagnetic metalmaterial which relatively easily causes exchange coupling betweenmagnetic films, for example, Cu, Ag or Au. In consideration of thestability against heat at the interface between the ferromagnetic film260 and the nonmagnetic film 270 and the interface between theferromagnetic film 280 and the nonmagnetic film 270, the nonmagneticfilm 270 is more preferably formed of, for example, Ru, Rh, Ir, or Re.Ru is especially preferable.

[0228] The ferromagnetic films 260 and 280 of the hard magnetic film 110as the exchange-coupled ferrimagnetic film are preferably formed of ametal magnetic material containing at least one of Ni, Co and Fe as amain component.

[0229] The exchange coupling between the ferromagnetic films 260 and 280can be made antiferromagnetic by forming the nonmagnetic film 270 tohave an appropriate thickness (for example, about 0.4 to about 1 nm).When the nonmagnetic film 270 is formed of Ru, the thickness of thenonmagnetic film 270 is about 0.6 nm or more and about 0.8 nm or less).In the case where the antiferromagnetic film (magnetization rotationprevention film) 180 is adjacent to the ferromagnetic films 260 and 280,the pinning effect can be improved.

[0230] The structures of the MR portion 100 shown in the fifth exampleare applicable to the MR portion 101 (FIG. 3) and the MR portion 102(FIGS. 6A and 6B).

[0231] The nonmagnetic insulating film 120 is preferably formed of anoxide such as, for example, Al₂O₃ or MgO, a carbide and a nitride. Thenonmagnetic insulating film 120 can also be formed of a wide-gapsemiconductor having an energy gap value of about 2 to about 6 eV.

[0232] Preferable metals usable for the nonmagnetic film 121 (FIG. 6A)include, for example, Cu, Ag, Au and Ru. Cu is especially preferable.

[0233] The nonmagnetic film 121 needs to have a thickness of at leastabout 0.9 nm in order to weaken the interaction between the magneticfilms interposing the nonmagnetic insulating film 120 or 121. Thethickness of the nonmagnetic film 121 needs to be about 10 nm or less,preferably about 3 nm or less since, otherwise, the MR ratio becomesexcessively low. When the thickness of the nonmagnetic film 121 is about3 nm or less, the flatness of film or layer is important. When theflatness is not sufficient, two ferromagnetic films which are supposedto be magnetically separated from each other by the nonmagnetic film 121are magnetically coupled to reduce the MR ratio and the sensitivity. Theheight of the roughness of an interface between the nonmagnetic film andeach of the ferromagnetic films is preferably about 0.5 nm or less.

[0234] The nonmagnetic insulating film 120 needs to have a thickness ofat least about 0.3 nm in order to guarantee the insulating property. Thethickness of the nonmagnetic insulating film 120 needs to be about 3 nmor less, since, otherwise, the tunneling current cannot flow. When thethickness of the nonmagnetic film 120 is about 3 nm or less, theflatness of film or layer is important. When the flatness is notsufficient, the nonmagnetic insulating film 120 is broken and causes atunneling leak or the two ferromagnetic films (hard magnetic film 110and the soft magnetic film 130) are magnetically coupled to reduce theMR ratio and the sensitivity. The height of the roughness of aninterface between the nonmagnetic film and each of the ferromagneticfilms is preferably about 0.5 nm or less, more preferably 0.3 nm orless.

[0235] The MR portion 100, 101 and 102 in the fifth example are eachusable as an MR effect element as in the first and second examples.

EXAMPLE 6

[0236] In a sixth example according to the present invention, a methodfor producing the MR effect memory cell 1000 described in the firstexample with reference to FIG. 1 will be described. In thisspecification, ratios used to indicate the composition are all atomicratios.

[0237] Referring to FIG. 1, the MR portion 100 was produced using, assputtering targets, Ni_(0.68)Co_(0.2)Fe_(0.12) (for the soft magneticfilm 130), Al (for the nonmagnetic insulating film 120), Al₂O₃ (for thenonmagnetic insulating film 120), and Co_(0.75)Pt_(0.25) (for the hardmagnetic film 110). For sputtering, a multi-origin sputtering apparatus(not shown) was used. The basic structure of the MR portion 100 wasNiCoFe (15)/Al₂O₃ (1.5)/CoPt (10). In such a representation of thestructure, the numeral in the parentheses represents the thickness(unit: nm), and “/” represents that the substances mentioned before andafter the “/” are combined. The thickness of each film or layer wascontrolled by a shutter.

[0238] Regarding a method for forming the nonmagnetic insulating film120 (Al₂O₃), the inventors attempted method A of forming an Al film andthen oxidizing the Al film and method B of sputtering Al₂O₃, andevaluated the resultant nonmagnetic insulating films obtained in bothmethods. For oxidation in method A, three methods were attempted: (i)natural oxidation in a vacuum tank, (ii) natural oxidation while beingmoisturized in a vacuum tank, and (iii) oxidation in plasma in a vacuumtank. The nonmagnetic insulating film obtained by any of the methods(methods A and B) was satisfactory.

[0239] After the MR portion 100 was produced, CoPt for the hard magneticfilm 110 was magnetized, and the MR ratio of the MR portion 100 wasmeasured at room temperature at an applied magnetic field of 100 Oe. TheMR ratio of the MR portion 100 obtained using method A was about 30%,and the MR ratio of the MR portion 100 obtained using method B was about18%. The magnetic field width generated by the MR portion 100 obtainedusing method A was about 5 Oe, and the magnetic field width generated bythe MR portion 100 obtained using method B was about 10 Oe. The size ofthe MR portion 100 in a planar direction thereof was about 0.25 μm TheMR effect memory cell 1000 shown in FIG. 1 was produced including the MRportion 100 produced using method A, having a higher MR ratio. Theconductive films 140 and 150 acting as a part of either a sense line anda bit line were formed of Pt or Au, and the conductive film 170 actingas a part of a word line was formed of, for example, Al, AuCr, Ti/Au,Ta/Pt, Cr/Cu/Pt/Ta or TiW. The insulation film 160 for insulating the MRportion 100 and the conductive film 170 was formed of, for example,CaF₂, SiO₂ or Si₃N₄.

[0240] The operation of the MR effect memory cell 1000 produced in thismanner was confirmed in the following manner.

[0241] A pulse current 531 shown in FIG. 9A was caused to flow in theconductive film 170 (word line) to magnetize the hard magnetic film 110in one direction. Then, a pulse current 532 shown in FIG. 9B was causedto flow in the conductive film 170, and a change in the voltage value(i.e., a change in the resistance value ΔR₅/Δt) of the MR effect memorycell 1000 measured through the conductive films 140 and 150 (sense lineand bit line) was monitored. As a result, a pulse 533 shown in FIG. 9Bcorresponding to the written information was detected. Thus, it wasfound that the desired MR effect memory cell 1000 using a nonmagneticinsulating film was realized.

EXAMPLE 7

[0242] In a seventh example according to the present invention, a methodfor producing the MR effect memory cell 2000 described in the secondexample with reference to FIG. 3 will be described.

[0243] The MR portion 101 was produced in a manner similar to thatdescribed in the sixth example.

[0244] Referring to FIG. 3, the MR portion 101 was produced using, assputtering targets, Co_(0.9)Fe_(0.1) (for the soft magnetic film 130),Al (for the nonmagnetic insulating film 120), Ni_(0.2)Fe_(2.8)O₄ (forthe ferromagnetic film 190), IrMn (for the antiferromagnetic film 180,i.e., the magnetization rotation prevention layer). The basic structureof the MR portion 101 was Co_(0.9)Fe_(0.1) (7)/Al₂O₃(1.8)/Ni_(0.2)Fe_(2.8)O₄ (10)/IrMn (15). The nonmagnetic insulating film120 of Al₂O₃ was formed by method A described in the sixth example.

[0245] The MR ratio of the MR portion 101 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 101 was about 26%. The size of the MR portion 101 in a planerdirection thereof was about 0.7 μm².

[0246] The MR effect memory cell 2000 shown in FIG. 3 was producedincluding the MR portion 101 in a manner similar to that described inthe sixth example. The conductive films 141 and 150 were formed of Au,and the conductive film, 170 was formed of AuCr. The insulation film 160was formed of SiO₂ in this example, but can be formed of, for example,CaF₂, Al₂O₃ or Si₃N₄.

[0247] The operation of the MR effect memory cell 2000 produced in thismanner was confirmed in the following manner.

[0248] A pulse current 541 shown in FIG. 10A was caused to flow in theconductive film 170 to magnetize the soft magnetic film 130 in onedirection. Then, a pulse current 542 shown in FIG. 10B was caused toflow in the conductive film 170, and a change in the voltage value (ΔV₁)of the MR effect memory cell 2000 measured through the conductive films141 and 150 was monitored. As a result, a voltage change 543 shown inFIG. 10B corresponding to the written information was detected. Thus, itwas found that the desired MR effect memory cell 2000 using anonmagnetic insulating film was realized.

EXAMPLE 8

[0249] In an eighth example according to the present invention, a methodfor producing the MR portion 100 described in the fifth example withreference to FIG. 8A will be described.

[0250] The MR portion 100 was produced in a manner similar to thatdescribed in the sixth example.

[0251] Referring to FIG. 8A, the MR portion 100 was produced using, assputtering targets, Co_(0.9)Fe_(0.1) (for the interface magnetic film220), Co (for the interface magnetic film 220 and the hard magnetic film110), Al for the nonmagnetic insulating film 120), and CoMnB (for theferromagnetic film 210). Two types of MR portions 100 were produced. Onetype had a first basic structure of CoMnB (1)/Co (1)/Al₂O₃ (1.5)/Co (2),and the other type had a second basic structure of CoFeB(1)/Co_(0.9)Fe_(0.1) (1)/Al₂O₃ (1.5)/Co (2). For both types of MRportions 100, the nonmagnetic insulating film 120 of Al₂O₃ was formed bymethod A described in the sixth example.

[0252] A substrate (not shown) on which the MR portion 100 was to beformed was formed of, for example, a Si substrate having a surfacethereof thermally oxidized or an Al₂O₃ TiC. On the substrate, a singlelayer film or a laminate film formed of, for example, Ta, Cu, NiFe or Ptin accordance with a purpose of use was provided as an underlying layer.On the underlying layer, the MR portion 100 was provided. On the MRportion 100, a single layer film or a laminate film formed of, forexample, Ta, Cu, NiFe or Pt in accordance with a purpose of use, wasprovided as a cap layer.

[0253] The MR ratio of each type of MR portion 100 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 100 having the first basic structure was about 32%. The MRratio of the MR portion 100 having the second basic structure was about29%. The size of the MR portion 100 in a planar direction thereof wasabout 0.25 μm².

[0254] The MR effect memory cells 1000 shown in FIG. 1 were producedincluding each type of MR portion 100. The conductive films 140 and 150were formed of Au and Cu, and the conductive film 170 was formed ofAuCr. The insulation film 160 for insulating the MR portion 100 and theconductive film 170 was formed of SiO₂ in this example, but can beformed of, for example, CaF₂, Al₂O₃ or Si₃N₄.

[0255] The operation of each type of MR effect memory cell 1000 producedin this manner was confirmed by the method described in the sixthexample with reference to FIGS. 9A and 9B. As a result, in both types ofMR effect memory cells 1000, the pulse 543 shown in FIG. 9Bcorresponding to the written information was detected. Thus, it wasfound that the desired MR effect memory cells 1000 according to thepresent invention was realized.

EXAMPLE 9

[0256] In a ninth example according to the present invention, a methodfor producing the MR effect memory cell 4000 described in the fourthexample will be described.

[0257] The MR portion 200 was produced in a manner similar to thatdescribed in the sixth example.

[0258] Referring to FIG. 7A through 7D, the MR portion 200 was producedusing, as sputtering targets, Ni_(0.68)Co_(0.2)Fe_(0.12) (for the softmagnetic films 132, 133 and 134), Al (for the nonmagnetic insulatingfilms 122, 123 and 124), and Co_(0.9)Fe_(0.1), Co and Co_(0.5)Fe_(0.5)(for the hard magnetic films 112, 113 and 114 having different magneticcoercive forces). The magnitudes of the magnetic coercive forces of thehard magnetic films have the relationship ofCo_(0.9)Fe_(0.1)>Co>Co_(0.5)Fe_(0.5).

[0259] The MR portion 200 had a three-layer structure ofNi_(0.68)Co_(0.2)Fe_(0.12) (10)/Al₂O₃ (1.5)/Co_(0.9)Fe_(0.1) (15)/Al₂O₃(15)/Ni_(0.68)Co_(0.2)Fe_(0.12) (10)/Al₂O₃ (1.5)/Co (15)/Al₂O₃(15)/Ni_(0.68)Co_(0.2)Fe₁₂ (10)/Al₂O₃ (1.5)/Co_(0.5)Fe_(0.5) (15). Thenonmagnetic insulating films 122, 123 and 124 of Al₂O₃ were formed bymethod A described in the sixth example.

[0260] The MR ratio of the MR portion 200 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 200 was about 28%. The size of the MR portion 200 in a planardirection thereof was about 0.25 μm².

[0261] The MR effect memory cell 4000 was produced including the MRportion 200 in a manner similar to that described in the sixth example.

[0262] The conductive films acting as a part of a sense line and a bitline (corresponding to the conductive films 140 and 150 in the firstexample; not shown in FIGS. 7A through 7D) were formed of Au, and theconductive film 172 was formed of AuCr. The insulation film 162 forinsulating the MR portion 200 and the conductive film 172 was formed ofSiO₂ in this example, but can be formed of, for example, CaF₂, Al₂O₃ orSi₃N₄.

[0263] The operation of the MR effect memory cell 4000 produced in thismanner was confirmed in the following manner.

[0264] A pulse current 551 shown in FIG. 11A was caused to flow in theconductive film 172 to magnetize the hard magnetic films 112, 113 and114 in one direction. Next, a pulse current 552 shown in FIG. 11B whichrises in a gradually increasing manner is caused to flow in theconductive film 172 to sequentially invert the magnetization directionsof the hard magnetic films 112, 113 and 114. A change in the voltagevalue (ΔV₂) was monitored through the sense line and the bit line. As aresult, a voltage change 553 shown in FIG. 11B corresponding to thewritten information was detected. Thus, it was found that multiplelevels of a signal were written in the MR effect memory cell 4000.

[0265] In the MR effect memory cell 4000 of the present invention,multiple level of a signal can be written by applying an appropriatebias current. Information written in the effect memory cell 4000 can beread based on a voltage change ΔV₂ occurring while a constant biasvoltage is applied.

EXAMPLE 10

[0266] In a tenth example according to the present invention, a methodfor producing the MR portion 100 described in the fifth example withreference to FIG. 8B will be described.

[0267] The MR portion 100 was produced in a manner similar to thatdescribed in the sixth example.

[0268] Referring to FIG. 8B, the MR portion 100 was produced using, astargets, Co_(0.9)Fe_(0.1) or Ni_(0.81)Fe_(0.19) (for the ferromagneticfilms 230 and 250 in the exchange-coupled ferrimagnetic film), Ru (forthe nonmagnetic film 240), Al (for the nonmagnetic insulating film 120),and Co_(0.9)Fe_(0.1) (for the hard magnetic film 110). Two types of MRportions 100 were produced. One type had a first basic structure ofCo_(0.9)Fe_(0.1) (1.9)/Ru (0.7)/Co_(0.9)Fe_(0.1) (2.9)/Al₂O₃(1.2)/Co_(0.9)Fe_(0.1) (20). The other type had a second basic structureof Ni_(0.8)Fe_(0.19) (3)/Ru (0.7)/Ni_(0.8)Fe_(0.19) (2)/Al₂O₃(1.2)/Co_(0.9)Fe_(0.1) (20). The nonmagnetic insulating film 120 ofAl₂O₃ was formed by method A described in the sixth example.

[0269] The MR ratio of each type of MR portion 100 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 100 of both types was about 25%. The size of the MR portion100 in a planar direction thereof was about 0.05 μm².

[0270] It was found that the MR portion 100 in this example has asmaller anti-magnetic force than a MR portion having a basic structureof Co_(0.9)Fe_(0.1) (4.8)/Al₂O₃ (1.2)/Co_(0.9)Fe_(0.1) (20) orNi_(0.8)Fe_(0.19) (5)/Al₂O₃ (1.2)/Co_(0.9)Fe_(0.1) (20). The MR portion100 in this example has a smaller anti-magnetic force because theinfluence of an anti-magnetic field is reduced by the structure shown inFIG. 8B.

[0271] The MR effect memory cell 1000 described in the first example wasproduced including each type of MR portion 100. The conductive films 140and 150 were formed of Au and Cu, and the conductive film 170 was formedof AuCr. The insulation film 160 for insulating the MR portion 100 andthe conductive film 170 was formed of SiO₂ in this example, but can beformed of, for example, CaF₂, Al₂O₃ or Si₃N₄.

[0272] The operation of the MR effect memory cell 1000 produced in thismanner was confirmed by the method described in the sixth example withreference to FIGS. 9A and 9B. As a result, in the MR effect memory cell1000 of both types, a pulse 533 shown in FIG. 9B corresponding to thewritten information was detected. Thus, it was found that the MR effectmemory cell 1000 according to the present invention was realized.

EXAMPLE 11

[0273] In an eleventh example according to the present invention, amethod for producing the MR effect memory cell 2000 described in thesecond example with reference to FIG. 3 will be described. The MR effectmemory cell 2000 produced in the eleventh example includes the softmagnetic film 130 described in the fifth example with reference to FIG.8B.

[0274] An MR portion 101 (FIG. 3) including the soft magnetic film 130shown in FIG. 8B was produced in a manner similar to that described inthe sixth example.

[0275] The MR portion 101 was produced using, as targets,Co_(0.9)Fe_(0.1) or Ni_(0.8)Fe_(0.19) (for the ferromagnetic films 230and 250 in the exchange-coupled ferrimagnetic film), Ru (for thenonmagnetic film 240), Al (for the nonmagnetic insulating film 120),Co_(0.5)Fe_(0.5) (for the ferromagnetic film 190), and IrMn (for theantiferromagnetic film 180, i.e., the magnetization rotation preventionlayer).

[0276] Two types of MR portions 101 were produced. One type had a firstbasic structure of Co_(0.9)Fe_(0.1) (1.9)/Ru (0.7)/Co_(0.9)Fe_(0.1)(2.9)/Al₂O₃ (1.2)/Co_(0.5)Fe_(0.5) (20)/IrMn (30). The other type had asecond basic structure of Ni_(0.81)Fe_(0.19) (3)/Ru(0.7)/Ni_(0.81)Fe_(0.19) (2)/Al₂O₃ (1.2)/Co_(0.5)Fe_(0.5) (20)/IrMn(30). The nonmagnetic insulating film 120 of Al₂O₃ was formed by methodA described in the sixth example.

[0277] The MR ratio of each type of MR portion 101 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 101 of both types was about 30%. The size of the MR portion101 in a planar direction thereof was about 0.05 μm².

[0278] It was found that the MR portion 101 in this example has asmaller anti-magnetic force than a MR portion having a basic structureof Co_(0.9)Fe_(0.1) (4.8)/Al₂O₃ (1.2)/Co_(0.5)Fe_(0.5) (20)/IrMn (30) orNi_(0.81)Fe_(0.19) (5)/Al₂O₃ (1.2)/Co_(0.5)Fe_(0.5) (20)/InMn (30). TheMR portion 101 in this example has a smaller anti-magnetic force becausethe influence of an anti-magnetic field is reduced by the structureshown in FIG. 8B.

[0279] The MR effect memory cell 2000 described in the second examplewas produced including each type of MR portion 101 having the softmagnetic film 130 shown in FIG. 8B in a manner similar to that describedin the sixth example. The conductive films 141 and 150 were formed of Auand Cu, and the conductive film 170 was formed of AuCr. The insulationfilm 160 for insulating the MR portion 101 and the conductive film 170was formed of SiO₂ in this example, but can be formed of, for example,CaF₂, Al₂O₃ or Si₃N₄.

[0280] The operation of the MR effect memory cell 2000 produced in thismanner was confirmed by the method described in the seventh example withreference to FIGS. 10A and 10B. As a result, in the MR effect memorycell 2000 of both types, the voltage change 543 shown in FIG. 10Bcorresponding to the written information was detected. Thus, it wasfound that the MR effect memory cell 2000 according to the presentinvention was realized.

[0281] The magnetization rotation prevention layer was formed of IrMn inthis example, but can be formed of PtMn, α-Fe₂O₃, NiO, orperovskite-based oxide such as, for example, YFeO₃ or SmFeO₃.

EXAMPLE 12

[0282] In a twelfth example according to the present invention, a methodfor producing the MR effect memory cell 1000 described in the firstexample with reference to FIG. 1 will be described. The MR effect memorycell 1000 produced in the twelfth example includes the soft magneticfilm 130 described in the fifth example with reference to FIG. 8B.

[0283] An MR portion 100 including the soft magnetic film 130 shown inFIG. 8B was produced in a manner similar to that described in the sixthexample. In this example, the nonmagnetic film 121 which is conductive(FIG. 6A) is used instead of the nonmagnetic insulating film 120. Thatis, the MR effect memory cell 1000 in this example is a GMR element.

[0284] The MR portion 100 was produced using, as targets,Ni_(0.68)Co_(0.2)Fe_(0.12) (for the ferromagnetic films 230 and 250 inthe exchange-coupled ferrimagnetic film), Cu (for the nonmagnetic film121), and Co_(0.9)Fe_(0.1) (for the hard magnetic film 110).

[0285] The MR portion 100 having a CPP structure had a basic structureof Co_(0.9)Fe_(0.1) (20)/Cu (3)/Ni_(0.68)Co_(0.2)Fe_(0.12) (2)/Ru(0.7)/Ni_(0.68)Co_(0.2)Fe_(0.12) (3).

[0286] The MR ratio of the MR portion 100 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 100 was about 16%. The size of the MR portion 100 in a planardirection thereof was about 0.05 μm².

[0287] The MR effect memory cell 1000 described in the first example wasproduced including the MR portion 100 having the soft magnetic film 130shown in FIG. 8B in a manner similar to that described in the sixthexample. The conductive films 140 and 150 were formed of Au and Cu, andthe conductive film 170 was formed of AuCr. The insulation film 160 forinsulating the MR portion 100 and the conductive film 170 was formed ofSiO₂in this example, but can be formed of, for example, CaF₂, Al₂O₃ orSi₃N₄.

[0288] The operation of the MR effect memory cell 1000 produced in thismanner was confirmed by the method described in the sixth example withreference to FIGS. 9A and 9B. As a result, the pulse 533 shown in FIG.9B corresponding to the written information was detected. Thus, it wasfound that the MR effect memory cell 1000 according to the presentinvention was realized.

EXAMPLE 13

[0289] In a thirteenth example according to the present invention, amethod for producing the MR effect memory cell 2000 described in thesecond example with reference to FIG. 3 will be described. The MR effectmemory cell 2000 produced in the thirteenth example includes the softmagnetic film 130 described in the fifth example with reference to FIG.8B.

[0290] The MR portion 101 (FIG. 3) including the soft magnetic film 130shown in FIG. 8B was produced in a manner similar to that described inthe sixth example. In this example, the nonmagnetic film 121 which isconductive (FIG. 6A) is used instead of the nonmagnetic insulating film120. That is, the MR effect memory cell 2000 in this example is a GMRelement.

[0291] The MR portion 101 was produced using, as targets,Ni_(0.68)Co_(0.2)Fe_(0.12) (for the ferromagnetic films 230 and 250 inthe exchange-coupled ferrimagnetic film), Cu (for the nonmagnetic film121), Co_(0.9)Fe_(0.1) (for the ferromagnetic film 190), and PtMn (forthe antiferromagnetic film 180, i.e., the magnetization rotationprevention layer).

[0292] The MR portion 101 having a CPP structure had a basic structureof PtMn (30)/Co_(0.9)Fe_(0.1) (20)/Cu(3)/Ni_(0.6)Co_(0.2)Fe_(0.12 ()2)/Ru (0.7)/Ni_(0.68)Co_(0.2)Fe_(0.12)(3).

[0293] The MR ratio of the MR portion 101 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 101 was about 19%. The size of the MR portion 101 in a planardirection thereof was about 0.05 μm².

[0294] The MR effect memory cell 2000 described in the second examplewas produced including the MR portion 101 having the soft magnetic film130 shown in FIG. 8B in a manner similar to that described in the sixthexample. The conductive films 141 and 150 were formed of Au and Cu, andthe conductive film 170 was formed of AuCr. The insulation film 160 forinsulating the MR portion 101 and the conductive film 170 was formed ofSiO₂ in this example, but can be formed of, for example, CaF₂, Al₂O₃ orSi₃N₄.

[0295] The operation of the MR effect memory cell 2000 produced in thismanner was confirmed by the method described in the seventh example withreference to FIGS. 10A and 10B. As a result, the voltage change 543shown in FIG. 10B corresponding to the written information was detected.Thus, it was found that the MR effect memory cell 2000 according to thepresent invention was realized.

EXAMPLE 14

[0296]FIG. 12A is a configuration diagram of an MRAM 5000 in afourteenth example according to the present invention. FIG. 12B is apartial isometric view of the MRAM 5000, and FIG. 12F is a partial planview of the MRAM 5000.

[0297] The MRAM 5000 includes a plurality of MR effect memory cells 1010in a matrix of 256×256 (row x column). The number of the MR effectmemory cells 1010 is optional.

[0298] As shown in FIG. 12B, the MR effect memory cell 1010 includes aword line 173 in addition to the structure of the MR effect memory cell1000 or 2000 described in the third example with reference to FIG. 5B.Preferably, the word lines 170 and 173 are respectively provided on atop surface and a bottom surface of the MR portion 100 or 101 as shownin FIG. 12B. The positions of the word lines 170 and 173 are not limitedto those shown in FIG. 12B, and the word lines 170 and 173 can bepositioned anywhere as long as a magnetic field can be effectivelyapplied to the MR portion 100 (or 101). FIGS. 12C, 12D and 12E showsexamples of the word lines 170 and 173.

[0299] In FIG. 12C, the word lines 170 and 173 are located offset withrespect to the MR portion 100 (or 101) by a certain angle to guaranteean effective application of a magnetic field to the MR portion 100 (or101). In this and any possible example according to the presentinvention, the word lines can be provided in a prescribed direction. Theprescribed direction is a row direction, a column direction, and adirection having an angle, for example, an angle of 45 degrees, withrespect to the row direction and the column direction. It is notnecessary for the word lines to be parallel to the sense lines and thebit lines.

[0300] In FIG. 12D, the sense line 140 is used instead of the word line170. In FIG. 12E, the word lines 170 and 173 are provided along sidesurfaces of the MR portion 100 (or 101). In the structure of FIG. 12E,currents are caused to flow in the word lines 170 and 173 in anidentical direction. A synthesized magnetic field is generated by theword lines 170 and 173. A synthesized magnetic field, which is made ofthe resultant synthesized magnetic field (generated by the word lines170 and 173) and a magnetic field generated by the sense line 140 (or141), is used for writing information to the MR portion 100 (or 101).

[0301] First, the MR effect memory cells 1010 including the word line173 in addition to the structure of the MR effect memory cell 1000 willbe described.

[0302] The MR portion 100 of the MR effect memory cells 1010 had astructure described in the tenth example, i.e., Ni_(0.81)Fe_(0.19)(3)/Ru (0.7)/Ni_(0.81)Fe_(0.19 ()2)/Al₂O₃ (1.2)/Co_(0.9)Fe_(0.1) (20).The inventors also produced another type of MR portion 100 having astructure of Ni_(0.81)Fe_(0.19) (2)/Ru (0.7)/Ni_(0.81)Fe_(0.19)(3)/Al₂O₃ (1.2)/Co_(0.9)Fe_(0.1) (20).

[0303] The conductive films 140 and 150 were formed of Au, Cu or Al, andthe conductive films 170 and 173 were formed of Cu. The insulation film160 for insulating the MR portion 100 (or 101) and the conductive film170 was formed of SiO₂ in this example, but can be formed of, forexample, CaF₂, Al₂O₃ or Si₃N₄.

[0304] As shown in FIG. 12A, the conductive films 140 and 150 (senselines and bit lines) are arranged in a lattice. The conductive films 170and 173 (word lines) are arranged in a lattice. Switching sections 301and 311 for address designation and signal detection sections 302 and312 are provided as shown in FIG. 12F. In FIG. 12F, the conductive films173 are not shown for clarity. The switching sections 301 and 311 selectarbitrary conductive films 140 and 150 and conductive films 170 and 173.The signal detection sections 302 and 312 detect the level of thecurrent or the value of the voltage of each conductive film.

[0305] Information is written in the MR portion 100 by causing a pulsecurrent to flow in one conductive film 170 and one conductive film 173(arranged in a lattice) and thus causing a magnetization state of aparticular MR portion 100 to be changed by a synthesized magnetic fieldgenerated by the one conductive film 170 and the one conductive film173.

[0306] Information write to and read from the MRAM 5000 is performedbasically in a manner same as that described in the sixth example withreference to FIGS. 9A and 9B. A read operation from the MRAM 5000 in anarbitrary information storage state was confirmed in the followingmanner.

[0307] A particular conductive film 140, a particular conductive film150, a particular conductive film 170, and a particular conductive film173 were selected by the switching sections 301 and 311. Whilemonitoring the resistance value of a MR portion 100 corresponding to theselected conductive films 140, 150, 170 and 173 (i.e., a selected MRportion 100), a magnetic field for causing magnetization inversion ofthe soft magnetic film 130 (FIG. 1) was applied to the selected MRportion 100. As a result, the pulse 533 shown in FIG. 9B was detectedthrough the signal detection section 302 or 312. Since the informationread was stored after the read, the read operation was confirmed to bean NDRO. Based on these results, it was found that the MRAM 5000according to the present invention was realized.

[0308] Next, the MR effect memory cells 1010 including the word line 173in addition to the structure of the MR effect memory cell 2000 describedin the eleventh example will be described.

[0309] The MR portion 101 of the MR effect memory cells 1010 had astructure described in the eleventh example, i.e., Ni_(0.81)Fe_(0.19)(3)/Ru (0.7)/Ni_(0.81) Fe_(0.19) (2)/Al₂O₃ (1.2)/Co_(0.5)Fe_(0.5)(20)/IrMn (30). The inventors also produced another type of MR portion101 having a structure of Ni_(0.81)Fe_(0.19) (2)/Ru(0.7)/Ni_(0.81)Fe_(0.19 ()3)/Al₂O₃ (1.2)/Co_(0.5)Fe_(0.5) (20)/IrMn(30).

[0310] The conductive films 141 and 150 were formed of Au and Cu, andthe conductive films 170 and 173 were formed of AuCr. The insulationfilm 160 for insulating the MR portion 101 and the conductive film 170was formed of SiO₂ in this example, but can be formed of, for example,CaF₂, Al₂O₃ or Si₃N₄.

[0311] As shown in FIG. 12A, the conductive films 141 and 150 (senselines and bit lines) are arranged in a lattice. The conductive films 170and 173 (word lines) are arranged in a lattice.

[0312] Information is written in the MR portion 101 by causing a pulsecurrent to flow in one conductive film 170 and one conductive film 173(arranged in a lattice) and thus causing a magnetization state of aparticular MR portion 101 to be changed by a synthesized magnetic fieldgenerated by the one conductive film 170 and the one conductive film173.

[0313] Information write to and read from the MRAM 5000 is performedbasically in the same manner as that described in the seventh examplewith reference to FIGS. 10A and 10B. A read operation from the MRAM 5000in an arbitrary information storage state was confirmed in the followingmanner.

[0314] A particular conductive film 141, a particular conductive film150, a particular conductive film 170, and a particular conductive film173 were selected by the switching sections 301 and 311. Whilemonitoring the resistance value of a MR portion 101 corresponding to theselected conductive films 141, 150, 170 and 173 (i.e., a selected MRportion 101), a magnetic field for causing magnetization inversion ofthe soft magnetic film 130 (FIG. 8B) was applied to the selected MRportion 101. The magnetization direction of the soft magnetic film 130indicates the direction of the magnetization direction differencebetween the ferromagnetic films 230 and 250 (FIG. 8B). As a result ofthe monitoring, the voltage change 543 shown in FIG. 10B was detectedthrough the signal detection section 302 or 312. Thus, it was found thatthe MRAM 5000 according to the present invention was realized.

EXAMPLE 15

[0315] In a fifteenth example according to the present invention, amethod for producing the MR effect memory cell 2000 described in thesecond example with reference to FIG. 3 will be described. The MR effectmemory cell 2000 produced in the fifteenth example includes the softmagnetic film 130 described in the fifth example with reference to FIG.8C.

[0316] The MR portion 101 including the soft magnetic film 130 shown inFIG. 8C was produced in a manner similar to that described in the sixthexample.

[0317] The MR portion 101 was produced using, as targets,Ni_(0.81)Fe_(0.19) (for the ferromagnetic films 230 and 250 in theexchange-coupled ferrimagnetic film), Ru (for the nonmagnetic film 240),Al (for the nonmagnetic insulating film 120), Co_(0.9)Fe_(0.1) (for theferromagnetic films 260 and 280 in the other exchange-coupledferrimagnetic film), and IrMn (for the antiferromagnetic film 180, i.e.,the magnetization rotation prevention layer).

[0318] The MR portion 101 had a basic structure of Ni_(0.81)Fe_(0.19)(3)/Ru (0.7)/Ni_(0.81)Fe_(0.19) (2)/Al₂O₃ (1.2)/Co_(0.9)Fe_(0.1) (2)/Ru(0.7)/Co_(0.9)Fe_(0.1) (2)/IrMn (20). The nonmagnetic insulating film120 of Al₂O₃ was formed by method A described in the sixth example.

[0319] The MR ratio of the MR portion 101 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 101 was about 36%. The size of the MR portion 101 in a planardirection thereof was about 0.1 μm².

[0320] It was found that the MR portion 101 in this example has asmaller anti-magnetic force than a MR portion having a basic structureof Ni_(0.81)Fe_(0.19) (5)/Al₂O₃ (1.2)/Co_(0.9)Fe_(0.1) (2)/Ru(0.7)/Co_(0.9)Fe_(0.1) (2)/IrMn (20). The MR portion 101 in this examplehas a smaller anti-magnetic force because the influence of ananti-magnetic field is reduced by the structure shown in FIG. 8C.

[0321] The MR effect memory cell 2000 described in the second examplewas produced including the MR portion 101 having the soft magnetic film130 shown in FIG. 8C in a manner similar to that described in the sixthexample. The conductive films 141 and 150 were formed of Au and Cu, andthe conductive film 170 was formed of AuCr. The insulation film 160 forinsulating the MR portion 101 and the conductive film 170 was formed ofSiO₂ in this example, but can be formed of, for example, CaF₂, Al₂O₃ orSi₃N₄.

[0322] The operation of the MR effect memory cell 2000 produced in thismanner was confirmed by the method described in the seventh example withreference to FIGS. 10A and 10B. As a result, the voltage change 543shown in FIG. 10B corresponding to the written information was detected.Thus, it was found that the MR effect memory cell 2000 according to thepresent invention was realized.

EXAMPLE 16

[0323] In a sixteenth example according to the present invention, amethod for producing the MR effect memory cell 2000 described in thesecond example with reference to FIG. 3 will be described. The MR effectmemory cell 2000 produced in the sixteenth example includes the softmagnetic film 130 described in the fifth example with reference to FIG.8C.

[0324] The MR portion 101 including the soft magnetic film 130 shown inFIG. 8C was produced in a manner similar to that described in the sixthexample.

[0325] The MR portion 101 was produced using, as targets,Ni_(0.81)Fe_(0.19) (for the ferromagnetic films 230 and 250 in theexchange-coupled ferrimagnetic film), Ru (for the nonmagnetic film 240),Al (for the nonmagnetic insulating film 120), Co_(0.9)Fe_(0.1) (for theferromagnetic films 260 and 280 in the other exchange-coupledferrimagnetic film), and IrMn (for the antiferromagnetic film 180, i.e.,the magnetization rotation prevention layer). An MR portion 101including another ferromagnetic film (not shown) at the interfacebetween the nonmagnetic insulating film 120 and the ferromagnetic film250 was also produced. The another ferromagnetic film was formed ofCo_(0.9)Fe_(0.1).

[0326] Two types of MR portions 101 were produced. One type had a firstbasic structure of Ni_(0.81)Fe_(0.19) (3)/Ru (0.7)/Ni_(0.81)Fe_(0.19)(2)/Al₂O₃ (1.2)/ Co_(0.9)Fe_(0.1) (2)/Ru (0.7)/ Co_(0.9)Fe_(0.1)(2)/IrMn (20). The other type had a second basic structure ofNi_(0.81)Fe_(0.19) (3)/Ru (0.7)/Ni_(0.18)Fe_(0.19) (2)/ Co_(0.9)Fe_(0.1)(0.5)/Al₂O₃ (1.2)/ Co_(0.9)Fe_(0.1) (2)/Ru (0.7)/ Co_(0.9)Fe_(0.1)(2)/IrMn (20). The nonmagnetic insulating film 120 of Al₂O₃ was formedby method A described in the sixth example.

[0327] The MR ratio of each type of MR portion 101 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 101 having the first basic structure was about 35%, and theMR ratio of the MR portion 101 having the second basic structure wasabout 37%. The size of the MR portion 101 in a planar direction thereofwas about 0.1 μm².

[0328] Each MR portion 101 was heat-treated. The MR ratio of the MRportion 101 having the second basic structure reached about 41% whenheated at about 280° C. This suggests that Co_(0.9)Fe_(0.1) contained inthe soft magnetic film 130 (free layer) suppresses mutual diffusion ofNi and Al in the Ni_(0.81)Fe_(0.19) and Al₂O₃ layers and thus stabilizesthe interface. The Co_(0.9)Fe_(0.1) layer preferably has a thickness ofabout 1 nm or less.

[0329] The MR effect memory cell 2000 described in the second examplewas produced including the MR portion 101 having the soft magnetic film130 shown in FIG. 8C in a manner similar to that described in the sixthexample. The conductive films 141 and 150 were formed of Au and Cu, andthe conductive film 170 was formed of AuCr. The insulation film 160 forinsulating the MR portion 101 and the conductive film 170 was formed ofSiO₂ in this example, but can be formed of, for example, CaF₂, Al₂O₃ orSi₃N₄.

[0330] The operation of the MR effect memory cell 2000 produced in thismanner was confirmed by the method described in the seventh example withreference to FIGS. 10A and 10B. As a result, the voltage change 543shown in FIG. 10B corresponding to the written information was detected.Thus, it was found that the MR effect memory cell 2000 according to thepresent invention was realized.

EXAMPLE 17

[0331] In a seventeenth example according to the present invention, amethod for producing the MR effect memory cell 1000 described in thefirst example will be described.

[0332] The MR portion 100 shown in FIG. 1 was produced in a mannersimilar to that described in the sixth example.

[0333] The MR portion 100 was produced using, as targets,Ni_(0.8)Fe_(0.2) (for the soft magnetic film 130), Al (for thenonmagnetic insulating film 120), and NiMnSb (for the hard magnetic film110). The MR portion 100 having a structure of Ni_(0.8)Fe_(0.2)(15)/Al₂O₃ (1.2)/NiMnSb (50) was produced on a sapphire c-facesubstrate. The nonmagnetic insulating film 120 of Al₂O₃ was produced bymethod A described in the sixth example.

[0334] The MR ratio of the MR portion 100 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 100 was about 40%. The size of the MR portion 100 in a planardirection thereof was about 0.25 μm².

[0335] In this example, a sapphire substrate was used, but asatisfactory NiMnSb film can be produced using a magnesium oxide (100)substrate.

[0336] In this example, NiMnSb was used as a material exhibiting asufficiently high magnetic polarization ratio. When PtMnSb or PdMnSb isused, a similarly high MR ratio is exhibited and thus a satisfactory MRportion can be provided.

[0337] The MR effect memory cell 1000 described in the first example wasproduced including the MR portion 100 in the sapphire c-face in a mannersimilar to that described in the sixth example. The conductive films 140and 150 were formed of Au and Cu, and the conductive film 170 was formedof AuCr. The insulation film 160 for insulating the MR portion 100 andthe conductive film 170 was formed of SiO₂ in this example, but can beformed of, for example, CaF₂, Al₂O₃ or Si₃N₄.

[0338] The operation of the MR effect memory cell 1000 produced in thismanner was confirmed by the method described in the sixth example withreference to FIGS. 9A and 9B. As a result, the pulse 533 shown in FIG.9B corresponding to the written information was detected. Thus, it wasfound that the MR effect memory cell 1000 according to the presentinvention was realized.

EXAMPLE 18

[0339] In an eighteenth example according to the present invention, amethod for producing the MR effect memory cell 1000 described in thefirst example will be described.

[0340] The MR portion 100 shown in FIG. 1 was produced in a mannersimilar to that described in the sixth example.

[0341] The MR portion 100 was produced using, as targets,Ni_(0.8)Fe_(0.2) (for the soft magnetic film 130), Al (for thenonmagnetic insulating film 120), and PtMnSb (for the hard magnetic film110). The MR portion 100 having a structure of Ni_(0.8)Fe_(0.)2(15)/Al₂O₃ (1.2)/PtMnSb (50) was produced on a sapphire c-facesubstrate. Then on magnetic insulating film 120 of Al₂O₃ was produced bymethod A described in the sixth example.

[0342] First, PtMnSb was epitaxially grown on the sapphire c-facesubstrate at a temperature of about 500° C. The resultant PtMnSb layerexhibited a (111) orientation as a result of lattice matching with thesapphire c-face substrate. Then, Al was deposited and oxidized to formAl₂O₃ as described in the sixth example. Then, Ni_(0.8)Fe_(0.2) wasdeposited, thereby forming the MR portion 100 having a structure ofNi_(0.8)Fe_(0.2) (15)/Al₂O₃ (1.2)/PtMnSb (50).

[0343] The MR ratio of the MR portion 100 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 100 was about 40%. The size of the MR portion 100 in a planardirection thereof was about 0.25 μm².

[0344] In this example, a sapphire substrate was used, but asatisfactory PtMnSb film can be produced using a magnesium oxide (100)substrate. It was found that when the magnesium oxide (100) substrate isused, a PtMnSb film exhibiting a (100) orientation is obtained due tolattice matching.

[0345] In this example, PtMnSb was used as a material exhibiting asufficiently high magnetic polarization ratio. When NiMnSb or PdMnSb isused, a similarly high MR ratio is exhibited and thus a satisfactory MRportion can be provided.

[0346] The MR effect memory cell 1000 described in the first example wasproduced including the MR portion 100 on the sapphire c-face in a mannersimilar to that described in the sixth example. The conductive films 140and 150 were formed of Au and Cu, and the conductive film 170 was formedof AuCr. The insulation film 160 for insulating the MR portion 100 andthe conductive film 170 was formed of SiO₂ in this example, but can beformed of, for example, CaF₂, Al₂O₃ or Si₃N₄.

[0347] The operation of the MR effect memory cell 1000 produced in thismanner was confirmed by the method described in the sixth example withreference to FIGS. 9A and 9B. As a result, the pulse 533 shown in FIG.9B corresponding to the written information was detected. Thus, it wasfound that the MR effect memory cell 1000 according to the presentinvention was realized.

EXAMPLE 19

[0348] In a nineteenth example according to the present invention, amethod for producing the MR effect memory cell 2000 described in thesecond example will be described.

[0349] The MR portion 101 shown in FIG. 3 was produced in a mannersimilar to that described in the sixth example.

[0350] The MR portion 101 was produced using, as targets,Ni_(0.8)Fe_(0.2) (for the soft magnetic film 130), Al (for thenonmagnetic insulating film 120), PtMnSb (for the ferromagnetic film190), and α-Fe₂O₃ (for the antiferromagnetic film 180, i.e., themagnetization rotation prevention layer).

[0351] First, α-Fe₂O₃ was grown on a sapphire c-face substrate. Thus,the MR portion 101 having a structure of Ni_(0.8)Fe_(0.2) (15)/Al₂O₃(1.2)/PtMnSb (25)/α-Fe₂O₃ (40) was formed. The nonmagnetic insulatingfilm 120 of Al₂O₃ was produced by method A described in the sixthexample.

[0352] The MR ratio of the MR portion 101 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 101 was about 40%. The size of the MR portion 101 in a planardirection thereof was about 0.25 μm² at the minimum.

[0353] In this example, PtMnSb was used as a material exhibiting asufficiently high magnetic polarization ratio. When NiMnSb or CuMnSb isused, a similarly high MR ratio is exhibited and thus a satisfactory MRportion can be provided.

[0354] The MR effect memory cell 2000 described in the second examplewas produced including the MR portion 101 on the sapphire c-face in amanner similar to that described in the sixth example. The conductivefilms 141 and 150 were formed of Au and Cu, and the conductive film 170was formed of AuCr. The insulation film 160 for insulating the MRportion 101 and the conductive film 170 was formed of SiO₂ in thisexample, but can be formed of, for example, CaF₂, Al₂O₃ or Si₃N₄.

[0355] The operation of the MR effect memory cell 2000 produced in thismanner was confirmed by the method described in the seventh example withreference to FIGS. 10A and 10B. As a result, the voltage change 543shown in FIG. 10B corresponding to the written information was detected.Thus, it was found that the MR effect memory cell 2000 according to thepresent invention was realized.

EXAMPLE 20

[0356] In a twentieth example according to the present invention, amethod for producing the MR effect memory cell 2000 described in thesecond example will be described. The MR effect memory cell 2000produced in the twentieth example includes the soft magnetic film 130described in the fifth example with reference to FIG. 8C.

[0357] An MR portion 101 including the soft magnetic film 130 shown inFIG. 8C was produced in a manner similar to that described in the sixthexample.

[0358] The MR portion 101 was produced using, as targets,Ni_(0.81)Fe_(0.19) (for the ferromagnetic films 230 and 250 in theexchange-coupled ferrimagnetic film), Ru (for the nonmagnetic film 240),Al (for the nonmagnetic insulating film 120), Co_(0.9)Fe_(0.1) (for theferromagnetic films 260 and 280 in the other exchange-coupledferrimagnetic film), and IrMn (for the antiferromagnetic film 180, i.e.,the magnetization rotation prevention layer).

[0359] The MR portion 101 having a structure of Ni_(0.81)Fe_(0.19)(3)/Ru (0.7)/Ni_(0.81)Fe_(0.19) (2)/Al₂O₃ (1.2)/ Co_(0.9)Fe_(0.1) (2)/Ru(0.7)/ Co_(0.9)Fe_(0.1) (2)/IrMn (20) was formed. The nonmagneticinsulating film 120 of Al₂O₃ was produced by method A described in thesixth example.

[0360] The MR ratio of the MR portion 101 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 101 was about 35%. The size of the MR portion 101 in a planardirection thereof was about 0.05 μm².

[0361] The MR effect memory cell 2000 described in the second examplewas produced including the MR portion 101 in a manner similar to thatdescribed in the sixth example. The conductive films 141 and 150 wereformed of Cu, and the conductive film 170 was formed of Cu. Theinsulation film 160 for insulating the MR portion 101 and the conductivefilm 170 was formed of SiO₂ in this example, but can be formed of, forexample, CaF₂, Al₂O₃ or Si₃N₄.

[0362] In order to confirm the high speed operation of the MR effectmemory cell 2000 produced in this manner, a pulse current 561 (FIG. 13)was caused to flow in the conductive film 170 (word line) and a pulsecurrent 562 (FIG. 13) was caused to flow in the conductive film 150(sense line in this case) to monitor a change in the voltage value ΔV₃of the MR portion 101. As a result, a voltage change 563 shown in FIG.13 corresponding to the written information was detected.

[0363] In this example, the magnetic field generated by an applicationof a current to the sense line is in an axial direction in whichmagnetization rotation is relatively difficult, and the magnetic fieldgenerated by an application of a current to the word line is in an axialdirection in which magnetization rotation is relatively easy. In otherwords, the MR portion 101 tends to be magnetized in the direction of amagnetic field generated by the word line than in the direction of amagnetic field generated by the sense line.

[0364] It was found that a difference in the output voltage appears byapplying a pulse current to the sense line and the word line atdifferent trigger timings. A larger pulse current was applied to theword line than to the sense line. The pulse width t_(s) of the pulsecurrent applied to the sense line is preferably about 0.1 ns or more,and the pulse width t_(w) of the pulse current applied to the word lineis preferably about 0.1 ns or more. A timing difference t_(d) of thepulse applied to the sense word line with respect to the pulse appliedto the sense line is preferably about 0.1 ns or more and about 50 ns orless. It was found that by applying the pulse to the word line and thesense line at different trigger timings, a sufficiently high MR ratio isguaranteed and thus a sufficiently high output is provided.

[0365] Such an output characteristic indicates that it is effective inproviding a sufficiently high output to apply a magnetic field in anaxial direction in which magnetization rotation is relatively difficultbefore a magnetic field is applied in an axial direction in whichmagnetization rotation is relatively easy, not to apply a magnetic fieldonly in the axial direction in which magnetization rotation isrelatively easy (or the axial direction in which magnetization rotationis relatively difficult), when the magnetization direction is rotated at180 degrees. It is considered that such a manner of magnetic fieldapplication causes a magnetic torque against the magnetization inversionin the axial direction, in which magnetization rotation is relativelyeasy, to be applied more easily.

[0366] The MR portion 101 can tend to be magnetized in the direction ofa magnetic field generated by the sense line than in the direction of amagnetic field generated by the word line.

[0367] When a magnetic field is applied using both a word line and asense line which are substantially perpendicular to each other, anasteroid-type magnetic field curve 1401 shown in FIG. 14 determines astrength H_(s) of the magnetic field generated by the sense line and astrength H_(w) of the magnetic field generated by the word line. Thus,application of a magnetic field using both of the word line and thesense line (or two word lines) perpendicular to each other can reducethe level of the current required to flow in the sense line and the wordline in order to generate a magnetic field as well as in order to selectthe address of a particular MR portion.

[0368]FIG. 15A shows a configuration diagram of an MRAM 6000 including aplurality of MR effect memory cells 2000 in a matrix of 512×512 (row xcolumn), and FIG. 15B is a partial plan view of the MRAM 6000. Thenumber of the MR effect memory cells 2000 is optional.

[0369] As shown in FIG. 15B, switching sections 401 and 411 for addressdesignation and signal detection sections 402 and 412 are provided. Theswitching sections 401 and 411 select arbitrary conductive films 141,150 and 170. The signal detection sections 402 and 412 detect the levelof the current or the value of the voltage of each conductive film. Theconductive films 141 and 150 (sense lines and bit lines) are arranged ina lattice as shown in FIG. 15A. The conductive films 170 and 173 (wordlines) are arranged in a lattice. The word line 170 is preferablyprovided on a top surface of the MR portion 101 as shown in FIG. 15B,but can be provided on a side surface of the MR portion 101 as shown inFIG. 15A. The position of the word line is not limited to those thatshown in FIG. 15B, and the word line can be positioned anywhere as longas a magnetic field is effectively applicable to the MR portion 101.

[0370] Information is written in the MR portion 101 by causing a pulsecurrent to flow in one conductive film 150 and one conductive film 170(arranged in a lattice) and thus causing a magnetization state of aparticular MR portion 101 to be changed by a synthesized magnetic fieldgenerated by the one conductive film 150 and the one conductive film170. In this example, the conductive film 150 (sense line) is usedinstead of the conductive film 173 (word line) shown in the fourteenthexample.

[0371] A read operation from the MRAM 6000 in an arbitrary informationstorage state was confirmed in the following manner.

[0372] A particular conductive film 141, a particular conductive film150, and a particular conductive film 170 were selected by the switchingsections 401 and 411. The resistance value of a MR portion 101corresponding to the selected conductive films 141, 150 and 170 (i.e., aselected MR portion 101) was monitored. As described in the secondexample, a difference between the resistance value of the selected MRportion 101 and the reference resistance value was monitored through adifferential circuit (not shown; preferably built into the signaldetection sections 402 and 412). Thus, the written state was readcorresponding to the difference. Based on these results, it was foundthat the MRAM 6000 according to the present invention was realized.

EXAMPLE 21

[0373]FIG. 16A is a partial isometric view of an MR effect head 7000including the tunneling MR portion 101 described in the second examplewith reference to FIG. 3. FIG. 16B is a cross-sectional view of the MReffect head 7000. The MR portion 101 in the MR effect head 7000 includesthe soft magnetic film 130 described in the fifth example with referenceto FIG. 8B.

[0374] The MR portion 101 was produced in a manner similar to thatdescribed in the sixth example.

[0375] The MR portion 101 was produced using, as targets,Co_(0.9)Fe_(0.1) or Ni_(0.81)Fe_(0.19) (for the ferromagnetic films 230and 250 in the exchange-coupled ferrimagnetic film), Ru (for thenonmagnetic film 240), Al (for the nonmagnetic insulating film 120),Co_(0.9)Fe_(0.1) (for the ferromagnetic film 190), and IrMn (for theantiferromagnetic film 180, i.e., the magnetization rotation preventionlayer).

[0376] The MR portion 101 having a structure of Ni_(0.81)Fe_(0.19)(3)/Ru (0.7)/Ni_(0.81)Fe_(0.19) (2)/Al₂O₃ (1.2)/ Co_(0.9)Fe_(0.1)(20)/IrMn (30) was formed. The nonmagnetic insulating film 120 of Al₂O₃was produced by method A described in the sixth example.

[0377] The MR ratio of the MR portion 101 was measured at roomtemperature at an applied magnetic field of 100 Oe. The MR ratio of theMR portion 101 was about 30%. The size of the MR portion 101 in a planardirection thereof was about 0.25 μm².

[0378] The MR effect head 7000 includes the tunneling MR portion 101, asubstrate 601, for a slider, formed of a sintered material containingAl₂O₃. TiC as a main component, shield layers 602 and 603, writingmagnetic poles 605 and 606 formed of a NiFe alloy, a coil 607 formed ofCu, and gap layers 608 formed of Al₂O₃. The gap layers 608 are locatedbetween two adjacent layers. The shield layers 602 and 603 each have athickness of about 1 μm. The writing magnetic poles 605 and 606 eachhave a thickness of about 3 μm. The gap layers 608 between the shieldlayer 602 and the MR portion 101 and between the shield layer 603 andthe MR portion 101 each have a thickness of about 0.1 μm, and the gaplayer 608 between writing magnetic poles 605 and 606 is about 0.2 μm.The distance between the conductive layer 150 and the writing magneticpole 605 is about 4 μm, and the coil 607 has a thickness of about 3 μm.

[0379] The MR portion 101 is located between the shield layers 602 and603, and is not exposed to a surface 604 of the MR effect head 7000.

[0380] A bias current is applied to the MR portion 101 through theconductive films 141 and 150. The soft magnetic films 130 and theferromagnetic film 190 are set to have magnetization directions directedperpendicular to each other. Thus, changes in the magnetizationdirection corresponding to reproduction signals are detected at asufficiently high sensitivity.

[0381]FIG. 17A is a plan view of a magnetic disk apparatus 8000including a plurality of MR effect heads 7000. FIG. 17B is across-sectional view of the magnetic disk apparatus 8000.

[0382] A magnetic recording medium 701 is formed of a Co—Ni—Pt—Ta alloy.The MR effect head 7000 is supported by a magnetic head supportingsection 702, and driven by a magnetic head driving section 703. Thetracking width of the MR effect head 7000 is set to be 5 μm.

[0383] The MR effect head 7000 according to the present invention has ahigher resistance change ratio than a GMR effect head which is aconventional CIPMR element. Accordingly, the MR effect head 7000 has asufficiently large reproduction output and thus is very effective as amagnetic head for reproduction. Since the magnetic disk apparatus 8000detected voltage changes corresponding to the information recorded inthe magnetic recording medium at a sufficiently high level ofsensitivity, it was found that the MR effect head 7000 according to thepresent invention was realized.

[0384] The MR portions 100, 101, 102 and 200 in all the examples in thisspecification are usable as an MR effect head as described in thisexample.

[0385] According to the present invention, a MR effect memory cell orelement using an antiferromagnetic film or hard magnetic film areprovided.

[0386] According to one aspect of the present invention, a free layer inwhich the magnetization direction is relatively easily rotatable by theexternal magnetic field includes a ferromagnetic film having a smallmagnetic coercive force even though being thin, and an amorphous film.According to another aspect of the present invention, a free layerincludes a synthesized ferrimagnetic film including ferromagnetic filmswhich are antiferromagnetically exchange-coupled to each other. Byforming the free layer to have such structures, the MR effect memorycell or element can operate at a sufficiently high sensitivity eventhrough being microscopic and also can have a sufficiently large outputeven when the level of the current is low. An MRAM including a pluralityof such MR effect memory cells arranged in a matrix and integrated at ahigh density can also be provided.

[0387] According to still another aspect of the present invention,information can be efficiently read from the MR effect memory cell. AnNDRO can be realized.

[0388] Various other modifications will be apparent to and can bereadily made by those skilled in the art without departing from thescope and spirit of this invention. Accordingly, it is not intended thatthe scope of the claims appended hereto be limited to the description asset forth herein, but rather that the claims be broadly construed.

What is claimed is:
 1. A magneto-resistive effect element, comprising: afirst ferromagnetic film; a second ferromagnetic film; and a firstnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film, wherein: the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field, and the firstferromagnetic film has an effective magnetic thickness of about 2 nm orless.
 2. A magneto-resistive effect element according to claim 1,wherein at least one of the first ferromagnetic film and the secondferromagnetic film has a magnetization direction in a planar directionthereof.
 3. A magneto-resistive effect element according to claim 1,wherein the second ferromagnetic film is formed of XMnSb, where X is atleast one element selected from the group consisting of Ni, Pt, Pd andCu.
 4. A magneto-resistive effect element according to claim 1, whereinthe first ferromagnetic film includes: an amorphous magnetic film, and athird ferromagnetic film in contact with the first nonmagnetic film andinterposed between the amorphous magnetic film and the first nonmagneticfilm.
 5. A magneto-resistive effect element according to claim 4,wherein the third ferromagnetic film has a thickness of about 0.2 nm ormore and about 2 nm or less.
 6. A magneto-resistive effect elementaccording to claim 4, wherein the third ferromagnetic film has athickness of about 0.8 nm or more and about 1.2 nm or less.
 7. Amagneto-resistive effect element according to claim 4, wherein theamorphous magnetic film includes at least one selected from the groupconsisting of CoFeB and CoMnB.
 8. A magneto-resistive effect elementaccording to claim 1, wherein the first ferromagnetic film includes: asecond nonmagnetic film, a fourth ferromagnetic film, and a fifthferromagnetic film, wherein the fourth ferromagnetic film and the fifthferromagnetic film are antiferromagnetically exchange-coupled with eachother through the second nonmagnetic film.
 9. A magneto-resistive effectelement according to claim 8, wherein the fourth ferromagnetic film andthe fifth ferromagnetic film have different strengths of saturatedmagnetization from each other.
 10. A magneto-resistive effect elementaccording to claim 8, wherein the fourth ferromagnetic film and thefifth ferromagnetic film have different thicknesses from each other. 11.A magneto-resistive effect element according to claim 10, wherein thefourth ferromagnetic film and the fifth ferromagnetic film have athickness difference of about 2 nm or less.
 12. A magneto-resistiveeffect element according to claim 8, wherein the second nonmagnetic filmis formed of Ru.
 13. A magneto-resistive effect element according toclaim 8, wherein the second nonmagnetic film is formed of one of Rh, Irand Re.
 14. A magneto-resistive effect element according to claim 12,wherein the second nonmagnetic film has a thickness of about 0.6 nm ormore and about 0.8 nm or less.
 15. A magneto-resistive effect elementaccording to claim 8, wherein at least one of the fourth ferromagneticfilm and the fifth ferromagnetic film contains at least one elementselected from the group consisting of Ni, Co and Fe as a main component.16. A magneto-resistive effect element according to claim 8, wherein thefourth ferromagnetic film and the fifth ferromagnetic film aremagnetization-rotated while being kept anti-parallel to each other. 17.A magneto-resistive effect element according to claim 1, wherein thesecond ferromagnetic film includes: a third nonmagnetic film, a sixthferromagnetic film, and a seventh ferromagnetic film, wherein the sixthferromagnetic film and the seventh ferromagnetic film areantiferromagnetically exchange-coupled with each other through the thirdnonmagnetic film.
 18. A magneto-resistive effect element according toclaim 17, wherein the third nonmagnetic film is formed of Ru.
 19. Amagneto-resistive effect element according to claim 17, wherein thethird nonmagnetic film is formed of one of Rh, Ir and Re.
 20. Amagneto-resistive effect element according to claim 18, wherein thethird nonmagnetic film has a thickness of about 0.6 nm or more and about0.8 nm or less.
 21. A magneto-resistive effect element according toclaim 17, wherein at least one of the sixth ferromagnetic film and theseventh ferromagnetic film contains at least one element selected fromthe group consisting of Ni, Co and Fe as a main component.
 22. Amagneto-resistive effect element according to claim 1, wherein the firstnonmagnetic film is an insulating film.
 23. A magneto-resistive effectelement according to claim 22, wherein the insulating film contains atleast one selected from the group consisting of Al₂O₃, MgO, a carbideand a nitride.
 24. A magneto-resistive effect memory cell, comprising: afirst ferromagnetic film; a second ferromagnetic film; a firstnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film; and at least one conductive film for causinga magnetization rotation of at least the first ferromagnetic film,wherein: the first ferromagnetic film has a magnetization more easilyrotatable than a magnetization of the second ferromagnetic film by anexternal magnetic field, and the first ferromagnetic film has aneffective magnetic thickness of about 2 nm or less.
 25. Amagneto-resistive effect memory cell according to claim 24, wherein atleast one of the first ferromagnetic film and the second ferromagneticfilm has a magnetization direction in a planar direction thereof.
 26. Amagneto-resistive effect memory cell according to claim 24, wherein thesecond ferromagnetic film is formed of XMnSb, where X is at least oneelement selected from the group consisting of Ni, Pt, Pd and Cu.
 27. Amagneto-resistive effect memory cell according to claim 24, wherein thefirst ferromagnetic film includes: an amorphous magnetic film, and athird ferromagnetic film in contact with the first nonmagnetic film andinterposed between the amorphous magnetic film and the first nonmagneticfilm.
 28. A magneto-resistive effect memory cell according to claim 27,wherein the third ferromagnetic film has a thickness of about 0.2 nm ormore and about 2 nm or less.
 29. A magneto-resistive effect memory cellaccording to claim 27, wherein the third ferromagnetic film has athickness of about 0.8 nm or more and about 1.2 nm or less.
 30. Amagneto-resistive effect memory cell according to claim 27, wherein theamorphous magnetic film includes at least one selected from the groupconsisting of CoFeB and CoMnB.
 31. A magneto-resistive effect memorycell according to claim 24, wherein the first ferromagnetic filmincludes: a second nonmagnetic film, a fourth ferromagnetic film, and afifth ferromagnetic film, wherein the fourth ferromagnetic film and thefifth ferromagnetic film are antiferromagnetically exchange-coupled witheach other through the second nonmagnetic film.
 32. A magneto-resistiveeffect memory cell according to claim 31, wherein the fourthferromagnetic film and the fifth ferromagnetic film have differentstrengths of saturated magnetization from each other.
 33. Amagneto-resistive effect memory cell according to claim 31, wherein thefourth ferromagnetic film and the fifth ferromagnetic film havedifferent thicknesses from each other.
 34. A magneto-resistive effectmemory cell according to claim 33, wherein the fourth ferromagnetic filmand the fifth ferromagnetic film have a thickness difference of about 2nm or less.
 35. A magneto-resistive effect memory cell according toclaim 31, wherein the second nonmagnetic film is formed of Ru.
 36. Amagneto-resistive effect memory cell according to claim 31, wherein thesecond nonmagnetic film is formed of one of Rh, Ir and Re.
 37. Amagneto-resistive effect memory cell according to claim 35, wherein thesecond nonmagnetic film has a thickness of about 0.6 nm or more andabout 0.8 nm or less.
 38. A magneto-resistive effect memory cellaccording to claim 31, wherein at least one of the fourth ferromagneticfilm and the fifth ferromagnetic film contains at least one elementselected from the group consisting of Ni, Co and Fe as a main component.39. A magneto-resistive effect memory cell according to claim 31,wherein the fourth ferromagnetic film and the fifth ferromagnetic filmare magnetization-rotated while being kept anti-parallel to each other.40. A magneto-resistive effect memory cell according to claim 24,wherein the second ferromagnetic film includes: a third nonmagneticfilm, a sixth ferromagnetic film, and a seventh ferromagnetic film,wherein the sixth ferromagnetic film and the seventh ferromagnetic filmare antiferromagnetically exchange-coupled with each other through thethird nonmagnetic film.
 41. A magneto-resistive effect memory cellaccording to claim 40, wherein the third nonmagnetic film is formed ofRu.
 42. A magneto-resistive effect memory cell according to claim 40,wherein the third nonmagnetic film is formed of one of Rh, Ir and Re.43. A magneto-resistive effect memory cell according to claim 41,wherein the third nonmagnetic film has a thickness of about 0.6 nm ormore and about 0.8 nm or less.
 44. A magneto-resistive effect memorycell according to claim 40, wherein at least one of the sixthferromagnetic film and the seventh ferromagnetic film contains at leastone element selected from the group consisting of Ni, Co and Fe as amain component.
 45. A magneto-resistive effect memory cell according toclaim 24, wherein the first nonmagnetic film is an insulating film. 46.A magneto-resistive effect memory cell according to claim 45, whereinthe insulating film contains at least one selected from the groupconsisting of Al₂O₃, MgO, a carbide and a nitride.
 47. Amagneto-resistive effect memory cell according to claim 24, wherein: atleast two layer structures are provided, each layer structure includingthe first ferromagnetic film, the second ferromagnetic film, and thefirst nonmagnetic film interposed between the first ferromagnetic filmand the second ferromagnetic film, and the at least two layer structuresare stacked with at least one fourth nonmagnetic film interposedtherebetween.
 48. A magneto-resistive effect memory cell according toclaim 47, wherein the second ferromagnetic films of the at least twolayer structures have different magnetic coercive forces from eachother.
 49. An MRAM, comprising a plurality of magneto-resistive effectmemory cells according to claim 24, wherein the plurality of conductivefilms are arranged in at least one prescribed direction.
 50. Amagneto-resistive effect element, comprising: a first ferromagneticfilm; a second ferromagnetic film; and a nonmagnetic film interposedbetween the first ferromagnetic film and the second ferromagnetic film,wherein: the first ferromagnetic film has a magnetization more easilyrotatable than a magnetization of the second ferromagnetic film by anexternal magnetic field, and the first ferromagnetic film includes: anamorphous magnetic film, and a third ferromagnetic film in contact withthe nonmagnetic film and interposed between the amorphous magnetic filmand the nonmagnetic film.
 51. A magneto-resistive effect elementaccording to claim 50, wherein at least one of the first ferromagneticfilm and the second ferromagnetic film has a magnetization direction ina planar direction thereof.
 52. A magneto-resistive effect elementaccording to claim 50, wherein the nonmagnetic film is an insulatingfilm.
 53. A magneto-resistive effect element, comprising: a firstferromagnetic film; a second ferromagnetic film; and a first nonmagneticfilm interposed between the first ferromagnetic film and the secondferromagnetic film, wherein: the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field, and the firstferromagnetic film includes: a second nonmagnetic film, a thirdferromagnetic film, and a fourth ferromagnetic film, wherein the thirdferromagnetic film and the fourth ferromagnetic film areantiferromagnetically exchange-coupled with each other through thesecond nonmagnetic film.
 54. A magneto-resistive effect elementaccording to claim 53, wherein at least one of the first ferromagneticfilm and the second ferromagnetic film has a magnetization direction ina planar direction thereof.
 55. A magneto-resistive effect elementaccording to claim 53, wherein the third ferromagnetic film and thefourth ferromagnetic film have different strengths of saturatedmagnetization from each other.
 56. A magneto-resistive effect elementaccording to claim 53, wherein the third ferromagnetic film and thefourth ferromagnetic film have different thicknesses from each other.57. A magneto-resistive effect element according to claim 53, whereinthe third ferromagnetic film and the fourth ferromagnetic film aremagnetization-rotated while being kept anti-parallel to each other. 58.A magneto-resistive effect element according to claim 53, wherein thesecond ferromagnetic film includes: a third nonmagnetic film, a fifthferromagnetic film, and a sixth ferromagnetic film, wherein the fifthferromagnetic film and the sixth ferromagnetic film areantiferromagnetically exchange-coupled with each other through the thirdnonmagnetic film.
 59. A magneto-resistive effect element according toclaim 53, wherein the first nonmagnetic film is an insulating film. 60.A magneto-resistive effect memory cell, comprising: a firstferromagnetic film; a second ferromagnetic film; a first nonmagneticfilm interposed between the first ferromagnetic film and the secondferromagnetic film; and at least one conductive film for causing amagnetization rotation of at least the first ferromagnetic film,wherein: the first ferromagnetic film has a magnetization more easilyrotatable the a magnetization of the second ferromagnetic film by anexternal magnetic field, and the first ferromagnetic film includes: anamorphous magnetic film, and a third nonmagnetic film in contact withthe first nonmagnetic film and interposed between the amorphous film andthe first nonmagnetic film.
 61. A magneto-resistive effect memory cellaccording to claim 60, wherein at least one of the first ferromagneticfilm and the second ferromagnetic film has a magnetization direction ina planar direction thereof.
 62. A magneto-resistive effect memory cellaccording to claim 60, wherein the first nonmagnetic film is aninsulating film.
 63. A magneto-resistive effect memory cell according toclaim 60, wherein: at least two layer structures are provided, eachlayer structure including the first ferromagnetic film, the secondferromagnetic film, and the first nonmagnetic film interposed betweenthe first ferromagnetic film and the second ferromagnetic film, and theat least two layer structures are stacked with at least one secondnonmagnetic film interposed therebetween.
 64. A magneto-resistive effectmemory cell according to claim 63, wherein the second ferromagneticfilms of the at least two layer structures have different magneticcoercive forces from each other.
 65. An MRAM, comprising a plurality ofmagneto-resistive effect memory cells according to claim 60, wherein theplurality of conductive films are arranged in at least one prescribeddirection.
 66. A magneto-resistive effect memory cell, comprising: afirst ferromagnetic film; a second ferromagnetic film; a firstnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film; and at least one conductive film for causinga magnetization rotation of at least the first ferromagnetic film,wherein: the first ferromagnetic film has a magnetization more easilyrotatable than a magnetization of the second ferromagnetic film by anexternal magnetic field, and the first ferromagnetic film includes: asecond nonmagnetic film, a third ferromagnetic film, and a fourthferromagnetic film, wherein the third ferromagnetic film and the fourthferromagnetic film are antiferromagnetically exchange-coupled with eachother through the second nonmagnetic film.
 67. A magneto-resistiveeffect memory cell according to claim 66, wherein at least one of thefirst ferromagnetic film and the second ferromagnetic film has amagnetization direction in a planar direction thereof.
 68. Amagneto-resistive effect memory cell according to claim 66, wherein thethird ferromagnetic film and the fourth ferromagnetic film havedifferent strengths of saturated magnetization from each other.
 69. Amagneto-resistive effect memory cell according to claim 66, wherein thethird ferromagnetic film and the fourth ferromagnetic film havedifferent thicknesses from each other.
 70. A magneto-resistive effectmemory cell according to claim 66, wherein the third ferromagnetic filmand the fourth ferromagnetic film are magnetization-rotated while beingkept anti-parallel to each other.
 71. A magneto-resistive effect memorycell according to claim 66, wherein the second ferromagnetic filmincludes: a third nonmagnetic film, a fifth ferromagnetic film, and asixth ferromagnetic film, wherein the fifth ferromagnetic film and thesixth ferromagnetic film are antiferromagnetically exchange-coupled witheach other through the third nonmagnetic film.
 72. A magneto-resistiveeffect memory cell according to claim 66, wherein the first nonmagneticfilm is an insulating film.
 73. A magneto-resistive effect memory cellaccording to claim 66, wherein: at least two layer structures areprovided, each layer structure including the first ferromagnetic film,the second ferromagnetic film, and the first nonmagnetic film interposedbetween the first ferromagnetic film and the second ferromagnetic film,and the at least two layer structures are stacked with at least onefourth nonmagnetic film interposed therebetween.
 74. A magneto-resistiveeffect memory cell according to claim 73, wherein the secondferromagnetic films of the at least two layer structures have differentmagnetic coercive forces from each other.
 75. An MRAM, comprising aplurality of magneto-resistive effect memory cells according to claim66, wherein the plurality of conductive films are arranged in at leastone prescribed direction.
 76. A method for writing information to andreading information from a magneto-resistive effect memory cell, themagneto-resistive effect memory cell including: a first ferromagneticfilm, a second ferromagnetic film, a nonmagnetic film interposed betweenthe first ferromagnetic film and the second ferromagnetic film, and atleast one conductive film, wherein the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field, the method comprisingthe steps of: causing a first current to flow in the at least oneconductive film to cause a magnetization rotation of at least the firstferromagnetic film, thereby writing information in the magneto-resistiveeffect memory cell; and causing a second current to flow in the firstferromagnetic film, the nonmagnetic film, and the second ferromagneticfilm; and causing a third current, which is a combination of a positivebias current and a negative bias current, to flow in the at least oneconductive film, thereby reading a voltage value corresponding to thesecond current and thus reading information written in themagneto-resistive element memory cell.
 77. A method according to claim76, wherein the third current has a level which causes a magnetizationrotation of the first ferromagnetic film but does not cause amagnetization rotation of the second ferromagnetic film.
 78. A methodfor writing information to and reading information from an MRAMincluding a plurality of magneto-resistive effect memory cells, eachmagneto-resistive effect memory cell including: a first ferromagneticfilm, a second ferromagnetic film, a nonmagnetic film interposed betweenthe first ferromagnetic film and the second ferromagnetic film, and atleast one conductive film, wherein the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field, the plurality ofconductive films being arranged in at least one prescribed direction,the method comprising the steps of: causing a first current to flow inthe at least one conductive film of a first magneto-resistive effectmemory cell of the plurality of magneto-resistive effect memory cells tocause a magnetization rotation of at least the first ferromagnetic filmof the first magneto-resistive effect memory cell, thereby writinginformation in the first magneto-resistive effect memory cell; andcausing a second current to flow in the first ferromagnetic film, thenonmagnetic film, and the second ferromagnetic film of the firstmagneto-resistive effect memory cell; and causing a third current, whichis a combination of a positive bias current and a negative bias current,to flow in the at least one conductive film of the firstmagneto-resistive effect memory cell, thereby reading a voltage valuecorresponding to the second current and thus reading information writtenin the first magneto-resistive effect memory cell.
 79. A methodaccording to claim 78, wherein the third current has a level whichcauses a magnetization rotation of the first ferromagnetic film but doesnot cause a magnetization rotation of the second ferromagnetic film. 80.A method according to claim 78, further comprising the step of causing afourth current to flow in the at least one conductive film of a secondmagneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell, the fourth current flowing in adirection for canceling a magnetic field leaked to a thirdmagneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.
 81. A method according to claim80, wherein the second magneto-resistive effect memory cell is identicalwith the third magneto-resistive effect memory cell.
 82. A method forreading information from a magneto-resistive effect memory cell, themagneto-resistive effect memory cell including: a first ferromagneticfilm, a second ferromagnetic film, a nonmagnetic film interposed betweenthe first ferromagnetic film and the second ferromagnetic film, and atleast one conductive film, wherein the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field, the method comprisingthe step of: causing a first current to flow in the first ferromagneticfilm, the nonmagnetic film, and the second ferromagnetic film; andcausing a second current, which is a combination of a positive biascurrent and a negative bias current, to flow in the at least oneconductive film, thereby reading a voltage value corresponding to thefirst current and thus reading information written in themagneto-resistive effect memory cell.
 83. A method according to claim82, wherein the second current has a level which causes a magnetizationrotation of the first ferromagnetic film but does not cause amagnetization rotation of the second ferromagnetic film.
 84. A methodfor reading information from an MRAM including a plurality ofmagneto-resistive effect memory cells, each magneto-resistive effectmemory cell including: a first ferromagnetic film, a secondferromagnetic film, a nonmagnetic film interposed between the firstferromagnetic film and the second ferromagnetic film, and at least oneconductive film, wherein the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film by an external magnetic field, the plurality ofconductive films being arranged in at least one prescribed direction,the method comprising the step of: causing a first current to flow inthe first ferromagnetic film, the nonmagnetic film, and the secondferromagnetic film of a first magneto-resistive effect memory cell ofthe plurality of magneto-resistive effect memory cells; and causing asecond current, which is a combination of a positive bias current and anegative bias current, to flow in the at least one conductive film ofthe first magneto-resistive effect memory cell, thereby reading avoltage value corresponding to the first current and thus readinginformation written in the first magneto-resistive effect memory cell.85. A method according to claim 84, wherein the second current has alevel which causes a magnetization rotation of the first ferromagneticfilm but does not cause a magnetization rotation of the secondferromagnetic film.
 86. A method according to claim 84, furthercomprising the step of causing a third current to flow in the at leastone conductive film of a second magneto-resistive effect memory cellother than the first magneto-resistive effect memory cell, the thirdcurrent flowing in a direction for canceling a magnetic field leaked toa third magneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.
 87. A method according to claim86, wherein the second magneto-resistive effect memory cell is identicalwith the third magneto-resistive effect memory cell.
 88. A method forwriting multiple levels of a signal to and reading multiple levels of asignal from a magneto-resistive effect memory cell, themagneto-resistive effect memory cell including: at least two layerstructures; at least one first nonmagnetic film interposed between theat least two layer structures; and at least one conductive film,wherein: each of the at least two layer structures includes a firstferromagnetic film, a second ferromagnetic film, and a secondnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film, and the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film, the method comprising the steps of: causing a firstcurrent in the at least one conductive film to cause a magnetizationrotation of at least one of the first ferromagnetic film and the secondferromagnetic film of each of the at least two layer structures, or tocause a magnetization rotation of none of the first ferromagnetic filmand the second ferromagnetic film of each of the at least two layerstructures, thereby writing multiple levels of a signal in themagneto-resistive effect memory cell; and causing a second current toeach of the at least two layer structures to compare a resistance valuecorresponding to the second current and a reference resistance value,thereby reading the multiple levels of the signal written in themagneto-resistive effect memory cell.
 89. A method according to claim88, further comprising the step of causing a current which rises in agradually increasing manner to flow in the at least one conductive film.90. A method for writing multiple levels of a signal to amagneto-resistive effect memory cell, the magneto-resistive effectmemory cell including: at least two layer structures; at least one firstnonmagnetic film interposed between the at least two layer structures;and at least one conductive film, wherein: each of the at least twolayer structures includes a first ferromagnetic film, a secondferromagnetic film, and a second nonmagnetic film interposed between thefirst ferromagnetic film and the second ferromagnetic film, and thefirst ferromagnetic film has a magnetization more easily rotatable thana magnetization of the second ferromagnetic film, the method comprisingthe steps of: causing a first current to flow in the at least oneconductive film to cause a magnetization rotation of at least one of thefirst ferromagnetic film and the second ferromagnetic film of each ofthe at least two layer structures, or to cause a magnetization rotationof none of the first ferromagnetic film and the second ferromagneticfilm of each of the at least two layer structures, thereby writingmultiple levels of a signal in the magneto-resistive effect memory cell.91. A method for reading multiple levels of a signal from amagneto-resistive effect memory cell, the magneto-resistive effectmemory cell including: at least two layer structures; at least one firstnonmagnetic film interposed between the at least two layer structures;and at least one conductive film, wherein: each of the at least twolayer structures includes a first ferromagnetic film, a secondferromagnetic film, and a second nonmagnetic film interposed between thefirst ferromagnetic film and the second ferromagnetic film, and thefirst ferromagnetic film has a magnetization more easily rotatable thana magnetization of the second ferromagnetic film, the method comprisingthe steps of: causing a first current to flow in each of the at leasttwo layer structures to compare a resistance value corresponding to thefirst current and a reference resistance value, thereby reading multiplelevels of a signal written in the magneto-resistive effect memory cell.92. A method according to claim 91, further comprising the step ofcausing a current which rises in a gradually increasing manner to flowin the at least one conductive film.
 93. A method for writing multiplelevels of a signal to and reading multiple levels of a signal from anMRAM including a plurality of magneto-resistive effect memory cells,each magneto-resistive effect memory cell including: at least two layerstructures; at least one first nonmagnetic film interposed between theat least two layer structures; and at least one conductive film,wherein: each of the at least two layer structures includes a firstferromagnetic film, a second ferromagnetic film, and a secondnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film, and the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film, the plurality of conductive films being arranged inat least one prescribed direction, the method comprising the steps of:causing a first current to flow in the at least one conductive film of afirst magneto-resistive effect memory cell of the plurality ofmagneto-resistive effect memory cells to cause a magnetization rotationof at least one of the first ferromagnetic film and the secondferromagnetic film of each of the at least two layer structures of thefirst magneto-resistive effect memory cell, or to cause a magnetizationrotation of none of the first ferromagnetic film and the secondferromagnetic film of each of the at least two layer structures of thefirst magneto-resistive effect memory cell, thereby writing multiplelevels of a signal in the first magneto-resistive effect memory cell;and causing a second current to flow in each of the at least two layerstructures of the first magneto-resistive effect memory cell to comparea resistance value corresponding to the second current and a referenceresistance value, thereby reading the multiple levels of the signalwritten in the first magneto-resistive effect memory cell.
 94. A methodaccording to claim 93, further comprising the step of causing a currentwhich rises in a gradually increasing manner to flow in the at least oneconductive film.
 95. A method according to claim 93, further comprisingthe step of causing a third current to flow in the at least oneconductive film of a second magneto-resistive effect memory cell otherthan the first magneto-resistive effect memory cell, the third currentflowing in a direction for canceling a magnetic field leaked to a thirdmagneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.
 96. A method according to claim95, wherein the second magneto-resistive effect memory cell is identicalwith the third magneto-resistive effect memory cell.
 97. A method forwriting multiple levels of a signal in an MRAM including a plurality ofmagneto-resistive effect memory cells, each magneto-resistive effectmemory cell including: at least two layer structures; at least one firstnonmagnetic film interposed between the at least two layer structures;and at least one conductive film, wherein: each of the at least twolayer structures includes a first ferromagnetic film, a secondferromagnetic film, and a second nonmagnetic film interposed between thefirst ferromagnetic film and the second ferromagnetic film, and thefirst ferromagnetic film has a magnetization more easily rotatable thana magnetization of the second ferromagnetic film, the plurality ofconductive films being arranged in at least one prescribed direction,the method comprising the steps of: causing a first current of flow inthe at least one conductive film of a first magneto-resistive effectmemory cell of the plurality of magneto-resistive effect memory cells tocause a magnetization rotation of at least one of the firstferromagnetic film and the second ferromagnetic film of each of the atleast two layer structures of the first magneto-resistive effect memorycell, or to cause a magnetization rotation of none of the firstferromagnetic film and the second ferromagnetic film of each of the atleast two layer structures of the first magneto-resistive effect memorycell, thereby writing multiple levels of a signal in the firstmagneto-resistive effect memory cell.
 98. A method according to claim97, further comprising the step of causing a second current to flow inthe at least one conductive film of a second magneto-resistive effectmemory cell other than the first magneto-resistive effect memory cell,the second current flowing in a direction for canceling a magnetic fieldleaked to a third magneto-resistive effect memory cell other than thefirst magneto-resistive effect memory cell.
 99. A method according toclaim 98, wherein the second magneto-resistive effect memory cell isidentical with the third magneto-resistive effect memory cell.
 100. Amethod for reading multiple levels of a signal from an MRAM including aplurality of magneto-resistive effect memory cells, eachmagneto-resistive effect memory cell including: at least two layerstructures; at least one first nonmagnetic film interposed between theat least two layer structures; and at least one conductive film,wherein: each of the at least two layer structures includes a firstferromagnetic film, a second ferromagnetic film, and a secondnonmagnetic film interposed between the first ferromagnetic film and thesecond ferromagnetic film, and the first ferromagnetic film has amagnetization more easily rotatable than a magnetization of the secondferromagnetic film, the plurality of conductive films being arranged inat least one prescribed direction, the method comprising the steps of:causing a first current to flow in each of the at least two layerstructures of a first magneto-resistive effect memory cell of theplurality of magneto-resistive effect memory cells to compare aresistance value corresponding to a the first current and a referenceresistance value, thereby reading multiple levels of a signal written inthe first magneto-resistive effect memory cell.
 101. A method accordingto claim 100, further comprising the step of causing a current whichrises in a gradually increasing manner to flow in the at least oneconductive film.
 102. A method according to claim 100, furthercomprising the step of causing a second current to flow in the at leastone conductive film of a second magneto-resistive effect memory cellother than the first magneto-resistive effect memory cell, the secondcurrent flowing in a direction for canceling a magnetic field leaked toa third magneto-resistive effect memory cell other than the firstmagneto-resistive effect memory cell.
 103. A method according to claim102, wherein the second magneto-resistive effect memory cell isidentical with the third magneto-resistive effect memory cell.